When the Dow's come down thousands of points in a matter of months, listening to some guy on TV telling you that this or that stock is cheap is going to get you killed, Cramer said. A lot of stocks look cheap after the market's taken such a beating, but that doesn't make them cheap. Besides, you know what happens to stocks that look cheap in an ugly market? They tend to get even cheaper.
Watch this video for Cramer's explanation of why valuation is the worst reason to buy a stock during a big downturn.
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