Consider that every instrument has a level that to important traders represents "value". When price drops below that level, these traders see something that's underpriced, even a bargain, and they begin to buy. At the other extreme, these traders see that the instrument is priced dearly, and buyers are thin on the ground, so they begin "taking profits", even exiting their positions entirely (this is what "support" and "resistance" are all about).
If you determine these levels for whatever it is you're trading, you'll recognize the signs that you should at least lighten up or exit entirely. And there's no psychological turmoil involved in exiting as long as you have a plan already laid out for re-entering the trade when price reaches a point where important traders consider it to be a "buy". Important traders do not, for example, abandon AAPL simply because it's had a correction. The ball is always in play, in one form or another.