Is 'letting winners run' ever just an excuse for not taking profits?

Been trying to get a handle on risk management and one thing I keep hearing is "let your winners run." Sounds great in theory, but I've watched a few really solid positions, like a recent $NVDA spike, give back a lot of their gains because I held on too long, convinced it was going to the moon. Or the next galaxy. Is there a point where you just have to admit you got a decent move and lock it in, even if it might go higher, or is that just being a bad trader? Seems like a fine line between conviction and just being greedy, or maybe stupid. How do you guys decide when enough is enough, or when to trim a position?