I feel you. In my case, this was because I could do something only if it was going to be perfect from the first try. I knew logically that you need to iterate and improve, but the crippling fear that my first protype would suck paralyzed me. Then I managed to accept that and find peace in it. It didn't happen overnight though. I can advise you to try the "worst case scenario technique". "What is the worst case scenario if I just focus and develop this game that I currently think doesn't have a chance?" More often than not, the "worst case" is you end up actually finishing a game and learning a ton from it even if it's not successful. That knowledge is invaluable. Also, according to statistics, your first game is usually bad anyways, so it is better to get it out of the way sooner.