If you can't convince yourself "When I'm down 25%, I'm a buyer" and banish forever the fatal thought "When I'm down 25%, I'm a seller," then you'll never make a decent profit in stocks. (Page 246, One Up On Wall Street)
If we are holding stock of a good company and if the price should decline, the logical thing for us to do is to buy more since the stock has become cheaper, especially if there is a good margin of safety. Why sell?
Remember that Peter Lynch is all about FA and I have no doubt that TA practitioners will be able to explain why selling might be a good idea based on chart action. Peter Lynch doesn't believe in stop loss, by the way.
I think, as retail investors, we have to take the middle ground. We probably do not have the financial muscles of a fund manager ......