In practice
Closing a winner feels good and closing a loser hurts, so traders tend to do the first too soon and the second too late. The result is small average wins and large average losses, the opposite of what a strategy needs.
Traders counter it by fixing the stop and the target before entry and placing both as orders, then checking in their journal how often they interfered.
What to watch for
It hides behind sensible-sounding words: taking profit is never wrong, or the trade just needs more time. Compare your actual average win and loss in R with the planned ones to see how much it costs you.