Here is a piece from Tim Harford on knowing when to persevere and when to quit ... which for us traders might well be phrased as 'should I stop out (or take profit!) or hold on?'
It's a good read, and while he doesn't specifically address trading, I think it can shed light on our behaviours. It might particularly be useful to newer entrants into this world of trading.
What's probably best about it, though, is 3 strategies he offers for dealing with the question. Not all may be applicable to to the 'get out or stay in' question, but hopefully its of interest.
With a title to the post like the one I have, Kenny Rogers may have been appropriate, but I'm going with The Clash: