Yes, the rule of thumb is you exit the trade when the price chart signals a trend reversal.
It’s difficult for you because your exit decisions are based on the open profit/loss and your feelings of fear (of winner turning into a loser) and greed (not wanting to exit too early) instead of what the chart is telling you.
Yes there is a right answer:
Ignore the open profit/loss and your feelings, focus on what the chart is telling you. The whole point of having a system, doing TA, using indicators, price action etc is to understand what the chart is telling you.