When we start winning we get anxious about loosing our gains .we close trades prematurely to capture the profits before the price starts to drop again.wereas we should be holding on to it and closing appropriately to maximize the profit.
Conversely,when we start loosing we hold on to the losing position longer in the hope it will turn upward at some point.we have the irrational beleif that we will reduce or wipe out the lose without proper re-analysis.
that's the mistake of novice traders who don't plan their trades as well as possible. they do not determine targets for profit and targets for loss limits. So what is done is only an estimate, not an analysis.
if they define profit and loss targets, they can exit the trade promptly. although sometimes people still have feelings of hoping to get more when they make a profit. If you are at a loss, you hope the movement will soon improve and reduce losses. Indeed, beginners are sometimes too influenced by that kind of thing.