Brain imaging studies show that investors as a whole get more and more used to big returns, and thus take bigger and bigger risks in a bull market--and then the bubble pops and stockholders start selling like mad.

FORBES: Psychology

Getting solid investment returns becomes more difficult as you get older because financial needs change.

FORBES: How We Sabotage Our Financial Decisions

For starters, companies with low ROE may get overlooked or beaten down more than warranted because of their lackluster returns.

FORBES: Magazine Article