When I'm moving around my laptop, and pop into the "projects" folder and see what a graveyard it has become. Dozens of half baked projects that seemed brilliant at the time, that I either lost interest in, decided the concept was too difficult, or (and this is the worst one) let my self doubt convince me that it would never work. The really sad part is, every now and then I'll go back in and check out these projects and a lot of the code and design is actually pretty good. I ask myself, "Why did I think this sucked again?"
The best analogy I can make to this scenario is the self doubt that cripples many writers setting out to finish a book, screenplay, or novel. It's almost as if you tell yourself that the script sucks, to give you a reason not to finish it and move on to something cooler next week. As a writer, what's the best way to overcome this? Just FINISH the god damned first draft. Roll up your sleeves, commit an hour (or two or three) every day to working on this project, and slog through it until you type "FADE OUT" (or "The End") or (if you're coding) make that glorious commit to polish off your project.
No matter how much the project, script or book sucks, there are few feelings of satisfaction that match that.