That can happen to a stock you bought at $300 and saw though to $650 to $700. Profits can dwindle away if you completely discount the possibility that past performance and an extraordinary present are not necessarily indicative of future results. When the writing on the wall starts turning into reality, don't let emotion keep you in a position out of spite. That's not a call to sell Apple today. It is, however, a piece of prudence to keep your head on straight and listen attentively when respectable figures such as Craig Barrett can't even stop talking about Steve Jobs. At the time of publication, the author was long FB. Follow @RoccoPendolaThis article is commentary by an independent contributor, separate from TheStreet's regular news coverage.