The fact that others are biased does not justify your disagreeing with them, if you have no reason to think you are much less biased. Via Brad DeLong, from a 2002 Fortune article by Justin Fox on "Is The Market Rational? No, say the experts. But neither are you–so don’t go thinking you can outsmart it:
The dirty little secret of the behavioralists is that, for all their work on investor irrationality and market anomalies, they still believe that markets work pretty well and that trying to outguess the collective wisdom of millions of investors is usually futile…. But efficient-markets theory has a dirty little secret, too, which is that for the market to remain efficient, there have to be lots of rational investors who believe enough in the market’s inefficiency to spend their careers trying to beat it….
The argument of modern behavioralists includes a crucial observation that wasn’t in Keynes–that professional investors are now under so much pressure from their customers that they cannot make the kind of long-term bets that might beat the market. If they do, as was the case with a lot of value-oriented mutual funds in the late 1990s, they can soon find themselves without any customers’ money to invest. That gets us to a world in which an investor with enough staying power and contrarian gumption can beat the market, but the vast majority of mutual funds and hedge funds don’t. In other words, the behavioralists have reconciled the success of a Warren Buffett (which efficient-markets purists have absurdly termed dumb luck) with the overwhelmingly empirical evidence that most professional money managers fail to beat the market.
This is, we posit, a major intellectual accomplishment. What does it mean for you? That’s easy: Buy and hold. Diversify. Put your money in index funds. Pay attention to the one thing you can control–costs–and keep them as low as possible.