It was hard paring down the list. After all, I can't think of a field that engenders more deceit than the one concerned with your wallet.

Just look at Madoff's $50 billion lie. Or take a gander at the rest of Wall Street and the moral depravity of the "liar loan" and other easy credit schemes. What sweet nothings were the mathematical models whispering to justify Bank of America's (NYSE:BAC) and Citigroup's subprime actions? How the heck can General Electric (NYSE:GE) and American Express (NYSE:AXP) be treated like banks for the purposes of government cheese?

But those aren't the biggest lies. They're too obvious, too well-known as lies. The real biggies are the ones we fall for over and over again, the ones that continue to suck our money right out of our wallets.

No. 5: Just about any prediction on CNBC
It pains me a little to say this, since Fools are frequent guests on these programs. Heck, we have CNBC on all day at Fool HQ.

Of course, we're usually poking fun at the reactionary, short-term thinking of the talking (nay, shouting) heads. Will there be a late-session rally? What's the outlook for retail in the next month? Does this week's unemployment report change everything? Does it matter?

Knee-jerk reactions are rarely profitable. Watch the financial news for entertainment and the latest financial goings-on. Don't watch it in hopes of discovering minute-by-minute market-timing tips.

No. 4: The idea that anything is a "safe investment"
No investment is 100% safe. None.

The bluest of the blue chips? They've cut dividends in record fashion the last few months -- and not just the financials, either. Dow Chemical (NYSE:DOW) and Harley-Davidson (NYSE:HOG) have both slashed their payouts recently.

Real estate is a no-brainer investment, because housing prices will rise forever? Apparently forever is shorter than we expected.

Even U.S. Treasuries are being called into question -- because they're just the latest asset bubble. Ironically, yields for Treasuries have been pushed down because people are flocking to what is widely considered the safest investment around -- but the prices of Treasuries will crater once the panic is gone and these yields shoot back up.

No. 3: "But this time it's different!"
I don't believe this line when it's spoken by people returning to bad relationships, and I don't believe it about questionable investments.

In fact, you can usually identify a bubble when you hear these words -- especially when they're followed by a faux-wise justification. I heard them during the dot-com bubble ("it's a new paradigm!"), during the housing bubble ("unlike other assets, housing prices never go down!"), and during the oil bubble last summer ("demand for oil will only go up!").

When you hear this line spoken by financial gurus, run, don't walk, from whatever it is they're recommending.

No. 2: "What's past is prologue …"
We must learn from history's mistakes, but we mustn't mistake history for the future.

For example, we all know about the tremendous returns U.S. stocks have produced over the last century, even factoring in this past lost decade.

But we can't simply extrapolate this performance out into the future. A hundred years ago, the U.S. was still in the relatively early stages of its economic development. Now it's a mature economy. Future returns will reflect that -- hence the importance of diversifying internationally into economies that resemble ours a century back.

And, finally, the No. 1 financial lie ...

No. 1: Your neighbor's a financial genius
It's easy to believe this one, since everyone has a great war story. Your neighbor identified Microsoft (NASDAQ:MSFT) in the late '80s before everyone caught on, or bought Google (NASDAQ:GOOG) right when it IPO'd. See the car in his driveway? He got it for well under invoice thanks to his shrewd negotiating. Or maybe he sold most of his stocks two years ago, brilliantly foreseeing all this economic turmoil.

I've got news for you. Your neighbor's an idiot.

OK, maybe he's not, but chances are he's not as smart as you think (or as he's telling you). The truth is, we only hear the good stuff. We never get a really good picture of people's finances. It's just not polite conversation to ask about your neighbor's salary, his credit card debt, or his true investment returns.

But you shouldn't get discouraged by the selective histories you hear. Financially speaking, it's never as good -- or as bad -- as people would have you believe.

Our retirement expert, Robert Brokamp, has seen this firsthand. He was a financial advisor before joining the Fool, so he's seen the reality of people's finances without all the bravado and whitewash.

And as the advisor of our Rule Your Retirement newsletter, he spends his days making sure we don't continue to fall for the financial lies spouting from the TV -- or our neighbors' mouths. He won't tell you his salary (I asked), but he does go through all the ins and outs of managing your finances, from allocating your portfolio to selecting the proper level of insurance to budgeting and taxes. You can read all his advice with a free 30-day trial. There's no obligation to subscribe.

Anand Chokkavelu owns shares of Citigroup and Microsoft. His neighbors think he's an idiot. Microsoft and American Express are Motley Fool Inside Value picks. Google is a Motley Fool Rule Breakers recommendation. Bank of America is a former Income Investor choice. The Fool owns shares of American Express and has a disclosure policy.