I've done this for as long as a can remember, in all aspects of life.
In my mind, there's nothing more pitiful than a person who tries his best and fails. Because that's the last thing I wish for, I rarely put much effort in things that I know could fail. When I do put a lot of effort, I usually don't make it known and act as if it was trivial.
In the end, the only work I'm proud to share with people is the one I never actually started. I've been chasing the same vision/ideal for more than 10 years, told everyone about it, and still haven't accomplished a thing. Fortunately, having done nothing prevents it from being a failure (in my mind), and the expected outcome is so great that nobody expects actual results anyways.
Now if only there was a fix that didn't involve a downgrade from thinker to doer.