Decide what you want from a trade. If you hit that, and get out with the profit you were after it was a good trade. Regardless of what happens afterwards.
FOMO = emotion = bad decisions.
This is especially true right now when arguably when the equity markets have detached from business fundamentals. Everyone one is chasing the next pump and dump. Don't be a bag holder!
That's true to some extent and the sentiment is certainly good advice, but learnings should also not be confused with regret or hindsight.
I sold two stagnant/marginally red funds in Jan 2020. I've reviewed all my holdings recently and also checked their performance since, which has been very poor. In fact they would be my only red funds if I still held them. I would therefore say that they were good trades/good decisions, purely as a result of that. I wouldn't regret selling them if they'd increased in value, but I'd still want to learn from it.
I've said it here before but it's an incredibly common mistake to hold on to losers and sell winners; it's much easier mentally to wish/hope for something to rise again rather than accepting defeat, and also much easier and a better feeling to cash in profits. As soon as I learnt to switch that mentality I've been far more successful with my decisions.