One of my failings as a Gamemaster, one truly bad habit my friends and players have told me I have, is that if the first few sessions of a campaign aren't quite right in my opinion, I'm likely to scrap the whole thing and start developing something else.
I acknowledge how annoying this can be for many gamers. You may have gotten behind the campaign premise, invested in your character, and after a few sessions (or even one session), the GM calls it quits saying it didn't really work for them. That can really turn one off to that particular GM, especially if it's happened more than once within say a few months or even a year.
I do this. Guilty as charged. I completely understand if this pisses any of my players off. I am truly sorry. I wish this weren't the case.
However...While I will endeavor to be more aware of it, I am unlikely to change.
If I am running a horror game, I expect it to feel frightening and suspenseful. If I am running an Anime/Manga style Giant Robot game, I am expecting it to feel like my favorite Mecha shows. If the feel or style is off, if the characters don't fit the setting, if the mechanics turn out to be more cumbersome than helpful, I would much rather cut my losses, the group's losses, and put my energy and efforts into something that will be more successful.
I know I could run a game and if I felt it wasn't working, just make some changes and then run it a few more times to hammer out the problems. That makes some sense but it isn't how my head works. If a game doesn't feel right I don't want to wait until I'm a dozen episodes in to realize its not good. I would see that as a colossal waste of time if I could have nipped it in the bud early and dedicated my efforts towards a better experience.
A common critique is that I am a perfectionist. If the game doesn't go exactly as I planned or foresaw it, I have to start over. This simply isn't true from my personal perspective. That's not how I look at it. I am not a perfectionist. I am not expecting it to be perfect. On the other head...remember the commercials I mentioned?
Fine might be good enough for the things you make. It isn't good enough for me. Just OK, is not OK.
I didn't get a reputation as a great GM by producing OK campaigns.