"Focus on the future productivity of the asset you are considering. [...] If you instead focus on the prospective price change of a contemplated purchase, you are speculating. There is nothing improper about that. I know, however, that I am unable to speculate successfully, and I am skeptical of those who claim sustained success at doing so. Half of all coin-flippers will win their first toss; none of those winners has an expectation of profit if he continues to play the game. And the fact that a given asset has appreciated in the recent past is never a reason to buy it."

-- Warren Buffett, in some thoughts on investing.