The last 12 months have been chock-full of scandalous financial headlines, and on four occasions we here at the Fool have dug in deep to find out how those headlines impact the market, the industry, and the average investor. From the collapse of MF Global to the Knight Capital (NYSE: KCG) flash crash, I've had the chance to interview investors on what keeps them up at night. What I've learned about what makes us nervous offers lessons in where the market is heading.

Paper trails can vanish
Initially, customers weren't especially concerned about MF Global's bankruptcy proceedings -- until $1.6 billion in segregated customer funds went missing. Nearly a year later, the customers have mostly been made whole, but it's been a long, rough ride. Cries for the head of Jon Corzine -- the former Goldman Sachs (GS 1.88%) executive turned MF Global CEO -- and executives of JPMorgan Chase (JPM 0.56%) who may have known about the missing money have gone unheeded; to date, no charges have been filed. This has left the CME Group (CME -0.71%), the Commodities Futures Trading Commission, and even the Department of Justice scrambling.

Lesson learned: The game can change overnight.

Blink and you'll miss it
Despite the media coverage proclaiming the end of high-frequency trading -- and thus, life as we know it -- the Knight Capital algorithm glitch left investors largely unaffected. There were exceptions, of course: Some investors who had a stop loss sell order on some stocks were startled to find their stocks had been sold and couldn't buy them back before the market course-corrected.

But those investors were the minority. Those who weren't actively micromanaging their portfolio, or who hadn't checked their Twitter or news feed until the end of the day, wouldn't have seen a thing.

Lesson learned: Keep calm and carry on.

Trading on insider information? Priceless.
"Either something was happening, or this was the greatest collection of investors seen in America," Congressman Tim Walz said about his decision to sponsor the STOCK Act. That elected officials could be profiting off insider information was something that hadn't ever occurred to most of us -- until Matt Koppenheffer cross-referenced disclosure statements with committee roles and found some startling coincidences, including an IPO participation in Visa (V -0.28%) that had very suspicious timing.

The STOCK Act was supposed to change that, but what ultimately passed was a version so watered down that it hasn't been mentioned since, except in lawsuits that want to strip its nearly nonexistent power.

Lesson Learned: There's always a loophole.

A toxic and destructive environment for customers
When Greg Smith resigned from Goldman Sachs with a letter in the International Herald Tribune bemoaning the giant's "toxic and destructive environment," we were captivated. And we immediately began investigating the large houses and interviewing the customers who worked with them. This led us into the financial advising and brokerage industry as a whole, where we heard stories running the gamut from heart-warming to bone-chilling. For some customers, being heard was a struggle; for others, working in sync with their advisor was nearly effortless. Everyone agreed, however, that clearly defined fees and expectations, as well as personal service, set apart the good advisors from the bad.

Lesson learned: Even if you know your money, you had better know your broker.

The Foolish bottom line
The headlines of the past year exposed flaws in long-held assumptions about financial regulation. The MF Global customers assumed their funds were safe because they were held in segregated accounts. Average constituents assumed their elected officials would never profit off an unfair advantage. People assumed their financial advisors and brokers held the same fiduciary responsibility. Investors put faith in an algorithm.

But while each case is different, the response has been consistent: a call for regulation. It's no longer enough to operate on trust; investors want clearer laws -- and consequences when those laws are broken. Whether that desire will translate into a change in the way we invest and how the markets operate remains to be seen. But the calls will continue and grow louder with each headline.

Nearly every bank or financial institution has made news this year -- most for nefarious reasons. There are six U.S. banks with more than $500 billion in total assets, and only one has managed to escape many of the scandals facing the other six. If you're looking to add one bank to your portfolio, you'll want to check out our special free report: "The Only Big Bank Built to Last." Download a copy today. It's free for Fools!