That things rarely go according to plan is part of running an RPG. The players will surprise you, and often this is entirely fine - in fact, it might result in a more memorable experience and a better game.
But sometimes, things go off the rail in a bad way - and you, as a GM, did not see it coming until it was too late, resulting in disaster and a non-fun experience for all concerned.
And contemplating some of my past mistakes, I am curious about your biggest GMing regrets. What went wrong, and what would you have done differently if you had the opportunity for a do-over?
I’m running a Cyberpunk RED campaign, and my players are motivated purely by money, revenge, and lust. I keep forgetting this and throwing scenarios at them with moral ambiguity, or the opportunity to help others.
Bless them for staying true to character. It makes hooks a little repetitive, however.