What I have learned is that players will make the game. As a GM you are the narrator. It is your job to catalog the player's adventure, not to run it. Sure, as the DM is is technically your game, but the players make it fun.

Example: In a Pokemon Tabletop game I am running (yes, laugh all you want), I gave them two baby Pokemon that happened to be sibilings. One made a run for it and ran towards the most injured character in the party. I had expected that they would attempt to catch it in my foolish GM mind. What did they actually do? She turned it into a crisp with her Pokemon. Unexpected? Yes. Not what I wanted? Yes. Does it make a hell of a lot better of a story? Yes.

It will be the crazy things the players do that they remember. Instead of them saying, "Remember when we recruited the crazy Centaur? Ya, that was fun," they'll be saying "Hey, remember when that prick of a Paladin stopped us from recruiting that Centaur? That sucked."