What’s your biggest investment disappointment flop after looking back after selling a Stock?

Basically, what is the worst decision that you made in selling something prematurely and how much money did you lose out on? I have a few but PLTR still kinda stings I had 100s of shares for about 5$ back In 2022 I think I sold em for 7$ right before it went insane price wise Ik it’s that not to bad but still… would love to hear other people‘s past pain and misery lol as long as we all learn something from it, right