http://turtletrader.com/pdfs/babe-ruth.pdf
'Say that you own four stocks, and that three of the stocks go down a bit but the fourth rises substantially. The portfolio will perform well even as the majority of the stocks decline.'
An obvious point, but one often overlooked IMHO, as it's easy to think you messed up when the market does the exact opposite of what you'd thought it would do!
Jeff