The fall of Lehman Brothers five years ago triggered a financial calamity that will never be forgotten by investors. We may have been bloodied initially by the turmoil, but we eventually emerged wiser about investing, in the end. Looking back at that tumultuous time, we asked our top investors to share their most valuable lesson from the financial crisis.

Seth Jayson: I learned, or rather, relearned, that things are only obvious in hindsight. Unfortunately, most investors cannot cope with this basic truth and will forever misunderstand recent market history and their place in it.

It's far too easy to look back at the credit spigot, the outright scam that masqueraded as a credit default industry, and the eventual unraveling and say, "I told you so!" Some smart observers had been telling us so for years before everything fell apart (and didn't make a nickel investing because their timing was wrong).

More difficult is looking back at the dark days at the bottom of the market and remembering that "only an idiot" was putting money to work then. If you were buying stocks and you didn't feel like an idiot, you weren't paying attention, because the financial press was telling you the worst was yet to come. And during the entire climb back, we've been told incessantly that the next leg down is just ahead. Luckily, the simplest investing policy is also the easiest to execute, even in those nausea-inducing times: Invest a little bit every month, regardless of market climate, into the best companies you can find. This served me well personally, and served us well at Hidden Gems, too.

Morgan Housel: You asked for one, but I'm going to give you five. I think they're all important: 

  • Cash gives you options. Debt takes options away. This is a simple way to think about the two, but it really captures what they do to your finances. 
  • It's much easier to say "I'll be greedy when others are fearful" than it is to actually do it. Almost everyone I know -- including myself -- should have bought more aggressively when stocks crashed. 
  • "Risk" in the stock market means different things to different people. The 2008-2009 crash was the biggest gift of opportunity investors may ever receive. 
  • Go back to early 2007. The majority of experts thought we'd avoid a recession. A few on the fringe foresaw trouble. An even smaller amount thought it would be bad. No one got the details right. Amazingly, this performance did nothing to dent the profession of forecasters. This should be remembered when listening to pundits. 
  • We went through the worst economic crisis in 80 years and it took just four years for stocks to return to all-time highs. This, too, should be remembered when the next big recession hits. 

David Gardner (as told to Chelsea Gustafson): First, an introduction for those unfamiliar: Motley Fool CAPS is our community stock-picking intelligence database. For more than seven years now, every 15 minutes our community's pick performance -- millions of picks -- are ranked and updated. Fully transparent, free, and accessible, CAPS thus provides a fishbowl view of the stock-picking activity of our community, based on a meritocratic system where what you do counts more than what you say. CAPS has been helping investors pick winners and avoid losers since its invention by David Gardner and our team in 2006.

On March 17, 2008, Lehman Brothers stock was trading at $30.50. Most of the smart money in the Motley Fool CAPS system had Lehman going nowhere but down. The Fool community stood in stark contrast to the uniformity of Wall Street players with their bullishness (green thumbs)... and red scores. That day, David decided to write this article, and side with the CAPS community. You may have heard that six months later, Lehman went bankrupt.

Catching up with David recently, he cited this article as one of his top 10 all-time favorite pieces of his own work. To think that Wall Street and the big money was buying Lehman, to think that The Motley Fool community intelligence was diametrically opposed, and to remember that literally within six months of his article Lehman was bankrupt spins a sad but deeply interesting yarn. 

On the five-year anniversary of Lehman's bankruptcy David vividly remembers his lesson learned: The spirit of CAPS, the spirit of The Motley Fool, is investors helping investors beat the market.

LouAnn Lofton: The most important investing lesson I learned from the financial crisis? That's easy -- controlling your emotions really is key to being an exceptional investor. Sure, I'd heard Buffett's oft-quoted quip about temperament mattering more than intellect (and I was even preparing to write a book on that very topic), but man, nothing brings the abstract into glaring, everyday reality like seeing your portfolio sliced in half.

I'd been investing for a decade prior to the fall of 2008. I'd been through the 2000 crash, through various market ups and downs, and I had a pretty good handle on my emotions. I think long-term, I don't pay attention to short-term blips, and I'm focused on owning shares of companies I believe in, versus trading tickers.

Nonetheless, the fall of 2008 and spring of 2009 presented me an opportunity to practice patience, calm, and long-term thinking like never before. It also served up chances to buy cheaper shares of companies I already owned (like Chipotle and Apple). I didn't panic, I didn't sell, and I actually bought more, but it was the scariest time as an investor I'd ever faced. Having made it through all that with my emotions -- and portfolio -- intact, I'm hopeful that I'll weather the next investing storm even better.

Alyce Lomax: Here's a sad lesson from the financial crisis: After scary times, many people learn little, some learn nothing at all, and way too many instead learned that they love a "good" bubble. We've seen too big to fail, too big to jail, and of course post-crisis merger mania left even bigger banks. Five years later, one might think it's just a matter of time before the next crisis. Remember the "green shoots" years ago? They didn't make it.

Even today, signs of economic recovery are fragile at best and delusional at worst. Fast zombies are terrifying, and the rampaging zombie bull market has been based on hope more than a real recovery for regular Americans, and floating many weak companies' stocks higher and higher. We "recovered" from the dot-com bubble with the housing bubble, and despite the scary events five years ago after that massive rupture, now apparently we have the bubble bubble for a soothing sense that good times are back. Be careful out there. When people refuse to learn anything, history repeats itself.

Alex Dumortier, CFA: Perhaps the most prominent lesson I've learned from the financial crisis is that just because you can't imagine something, doesn't mean it can't occur.

I remember early on in the crisis -- it must have been the end of 2007 or early 2008 -- discussing investment banks' position with a then-Motley Fool colleague. He was convinced it was catastrophic, but I simply could not conceive that an institution like Bear Stearns -- which was founded in 1923 and had achieved its fifth consecutive year of record profits in 2006 -- could fail. Clearly, the firm's pedigree and recent track record had blinded me to the obvious truth of excessive leverage and the simple dynamics that underlie a run on the bank, for Bear Stearns would surely have shared Lehman Brothers' fate if JPMorgan Chase (NYSE: JPM) had not swooped it up for a mere $10 per share.

My broad takeaway: Particularly in high-uncertainty situations, it's never a waste of time to question the basic assumptions behind your analysis and to try to flesh out alternative scenarios, particularly the ones you consider to be unlikely or even impossible (they never are).

Jim Mueller: Keep an investing journal. I write down several things in my journal: what I'm thinking, how I'm feeling (for instance, don't invest while still fuming over that driver who wouldn't budge), investments I'm considering, and so on. Essentially, it's a conversation about investing I hold with myself.

One thing I write is the reason I'm buying stock before I do so. This keeps me on a more even keel, because it forces me to think through each investment decision rather than reacting to the moment. I also write down how much I'm investing, once I make up my mind. This helps me track how much I commit to each position.

During that scary time, I was able to thoughtfully invest in several strong companies whose stock prices were down. And the journal showed – when later I thought I had "missed the bottom" –that I really was investing more heavily near the bottom. In fact, I put the most money to work in January and February 2009.

I really was buying when others were fearful (which proved to me that I could), something which has helped tremendously both then and later.

Charly Travers: The crisis highlighted the importance of investing in businesses that do not depend upon the kindness of others. If a company needs access to capital during a time of market stress, it will find that raising money is either very expensive or, in a worst-case scenario, not available at all. Needless to say, the shares of a company in this situation will get battered.

Fortunately, it is easy for Fools to avoid getting caught up in one of these vicious downward spirals. Only own shares of companies that employ conservative levels of debt financing. You don't want to be in a position where a company cannot refinance a large near-term maturity or is at risk of breaching debt covenants with the slightest downturn in its financials. Instead, look to own companies with cash-rich balance sheets and strong consistent free cash flow generation. You'll sleep better at night knowing you don't have ticking time bombs in your portfolio.

Matt DiLallo: I lost so much money during the financial crisis that I couldn't take it anymore. It was late February of 2009 and after dutifully saving and investing for years, it was time to take a break. It was time to turn off the TV, put down the paper, and just walk away. So for the months of March and April I didn't buy one share, nor did I contribute one dollar to my investment accounts.

While I admit the break from the noise was nice, I also missed the beginning of the greatest stock market recovery in my lifetime. Thankfully, I hadn't fallen into the temptation to sell everything so I was rather fully invested and was able to catch most of it. In fact, my current net worth is now four times higher than it was before the beginning of the financial crisis, but the lesson I learned is real clear: Timing the stock market is a fool's errand.

While I lamented that every stock I'd ever bought had lost money, it really didn't matter because it would be decades before I'd ever need any of it. That's why I now continue to press on and invest, no matter if the market is up or down. Because there is wisdom in the saying...It's not timing the market, but time in the market that leads to investing success.

Chuck Saletta: The most important lesson I learned is the power of a solid balance sheet to protect a company's survivability when its plans falter. Prior to the crisis, I barely paid any attention to the balance sheet. Then, General Electric (NYSE: GE) nearly fell apart during the crisis due to the heavy leverage on its balance sheet in spite of holding a coveted AAA debt rating at the time.

There was nothing quite like watching one of the largest and seemingly strongest companies around nearly choke on excessive debt to drive home just how important balance sheets are. After watching that mess unfold, I started incorporating tighter balance sheet checks in my buy and sell decision criteria, and thus far, that change has served me well.

Isaac Pino: Never invest in an industry where the incentives are broken. For now, I think Wall Street remains beyond repair.

The recent financial crisis followed a familiar storyline: A run-up in real estate prices led to widespread speculation, and suddenly, unexpectedly, the floor fell out from under us. While it's true that Americans from all walks of life contributed to the hysteria, it was the casino-like operations of the big banks that derailed the economy.

From my perspective, not much has changed on Wall Street to-date. Sure, the banks have reduced debt levels, or "deleveraged." We all have. But it's not clear that regulators -- let alone investors or the American public -- really understand the complex machinery that still runs Wall Street.

As we pointed out earlier this year, a recent survey found that "more than half of institutional investors did not trust how banks measure the riskiness of their assets." And JPMorgan, hailed by many as one of the best-managed banks during the crisis, is currently facing a $6 billion lawsuit from regulators over bad mortgage loans.

What occurred in 2008 was a perfect storm that wreaked havoc on both Main Street and Wall Street. I believe Main Street has learned a difficult lesson over the past five years and cleaned up its balance sheet. I can't say the same for Wall Street.

Patrick Morris: Five years ago I was learning firsthand in my college classes of the financial industry that was seemingly collapsing all around me. We learned stocks were supposedly priced to be the present value of their future cash flows; the market was efficient and no one could beat it; and if interest rates go up, bond prices go down. Yet while we learned from the textbooks, we also learned firsthand while doing case studies on mortgage-backed securities, and trying to wrap our heads around collateralized debt obligations.

Yet one indelible lesson I learned was that for an investor who is investing over a 30-to-40-year horizon, the market has historically returned an average of a little over 7% each year. By simply investing $25 a month in the S&P 500 from Sept. 2, 2008, until today you would have received a little over 8% annually. Even in the midst of wild market fluctuations in a period entitled "The Great Recession," the historical trend held true, and returns were available to those who simply trusted in the market and didn't attempt to time it.

Frank Thomas: You're never as contrarian as you think. We all like to pretend that we have the iron stomach of Warren Buffett and that we'd recognize it when it starts raining gold, but when the crap really hits the fan, we'll freeze just like anyone else. Had more banks failed and AIG crumbled, we would have entered a depression and those seemingly brave investments would have turned to dust.

In fact, the only way to take advantage of a panic is to prepare ahead of time. Build a shopping list during the good times so you're not relying on emotional analysis. Keep an opportunity fund, so you're not selling losers to buy more potential losers. And, keep enough cash to cover living expenses, so when the opportunity comes, you're not choosing between losing your portfolio and losing your next meal.

John Divine: I was in college studying finance in the fall of 2008 when I noticed something odd. Suddenly everyone cared about the stock market. 

The enormity of the crisis hit me in philosophy class. Instead of launching into a rant on the mind-body problem, my professor gave uncharacteristic pause, before saying this: 

"The Dow fell 700 points today. Welcome to The Great Depression 2.0."

I came home for Thanksgiving break a shaken young man; certain my degree would be worthless. I imagined myself peddling apples door-to-door after college. This was a shame, since I'd painstakingly built up a small stock portfolio.

"I'm out," I told my dad over the break. "I'm selling all my stocks."

He looked at me quizzically. He clearly didn't understand.

"Don't you see, Dad? We're in The Great Depression 2.0!" 

"Now is the worst time to sell your stocks," my dad said simply. "Hold onto them, and you'll be glad you did."

I held, and I'm glad I did. Fear is a powerful and costly emotion in investing. Take a step back; look at the long-term picture. And when philosophy professors start giving sweeping macroeconomic predictions, take them with a grain of salt.

Joe Tenebruso: I often think back to the days during the depths of the financial crisis, and I remember the feelings of despair, hopelessness, and even anger. But I also remember a light that shined through the darkness, and that was The Motley Fool. While other financial sites were shouting "PANIC" and "CRASH" and mercilessly displaying the blood red color of plunging stock prices, The Fool displayed the word "Opportunity" in bright green letters on the front page of Fool.com.

I remember how this simple, seemingly minor action made such a major difference in my perception of the market forces at play at the time. And this newfound mind-set greatly aided me in gaining the belief that, "This too shall pass."

Rather than panicking and selling my stocks at the depths of the market crash -- as so many fearful investors did at the time -- I moved most of my capital into dominant, financially sound businesses such as Google and Apple, and steeled myself with the resolve that I would ride out the financial crisis with my capital invested in some of the strongest businesses in the world. In time, this strategy would form the foundation of my Tier 1 investment philosophy.

Jake Keator: Imagine yourself at the age of 17 with a boatload of cash that you've dutifully saved since you first heard of an allowance. Now imagine those hard-earned savings chopped in half. That's exactly what happened to me when I invested all of my money in August of 2008, one month before Lehman declared bankruptcy.

It was the best thing that could have happened. At the age of 17, a boatload of cash was really just a couple thousand dollars, which was a small price to pay for the most important lesson I've ever learned about investing. Did I sell my deflated holdings and take the loss? No, I decided to wait, and the longer I waited, the easier it became to practice the hardest part of a buy-and-hold investment strategy: the holding.

Five years later, I am happy to say that my portfolio recovered, but more importantly, it taught me that investing takes time. There will be more stock market crashes before I retire, but this lesson will carry me through them all and hopefully lead to an actual boatload of cash down the road.

Anders Bylund: You don't have to see a huge market crash coming before setting up a cash reserve in your retirement account. Some fresh powder in your musket can come in handy at any time, and it doesn't always make sense to free up capital when you need it by selling stocks.

The Lehman bust caught me flat-footed. All of a sudden, I had a veritable smorgasbord of tempting values in front of me, most of them unlikely to go belly up. But I was also fully invested. I'd hate to sell plunging shares in order to pick up another deep value opportunity, because the stock I'm selling should also rebound strongly from temporary panic-sale levels.

So I've made it a habit to keep about 10% of my retirement account in super-liquid money market assets. You know, the interest-bearing portion of your 401(k) or IRA that you think of as "cash." That way, I'm always ready to pounce on the next shocking discount, whether it's a company-specific knee-jerk reaction or a marketwide panic like the 2008 debacle.

The fundamentally strong tickers out there can recover from almost any disaster, real or imagined. It pays to be ready when it happens.

John Reeves: The most valuable lesson I learned reinforced something I had read by Seth Klarman. Writing at the time, Klarman pointed out that "not all declines are equal" and that "buying early on the way down looks a great deal like being wrong, but it isn't."

During the worst of the crisis in 2008, everything went down regardless of the quality of the underlying business. We now know, in retrospect, that this was a tremendous time to buy excellent companies. But it sure didn't feel that way at the time.

Here are a couple of examples: from the beginning of 2008 until November 2008, Starbucks (NASDAQ: SBUX) was down 35% and Apple (NASDAQ: AAPL) was down 45%. If investors had somehow been able to ignore the scary market collapse, however, they'd be sitting on huge gains since the beginning of 2008 until now with Starbucks up 284% and Apple up 154% during that time frame.

The lesson here isn't, "darn, if only I had bought those stocks..." Rather, the real takeaway is that during 2008 two great businesses were unfairly punished by a gigantic macro event, and that mispricing resulted in a huge opportunity for level-headed investors.

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The Motley Fool recommends American International Group, Apple, Chipotle Mexican Grill, Google, and Starbucks. The Motley Fool owns shares of American International Group, Apple, Chipotle Mexican Grill, General Electric Company, Google, JPMorgan Chase & Co., and Starbucks and has the following options: long January 2014 $25 calls on American International Group. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.