A lot of people like to repeat the idea that "failure is a learning experience" but it is only recently that the
essence of this idea in practical terms became concrete for me (thanks to "177 Mental Toughness Secrets of the World Class"): you need to be
prepared to fail, which - among other things - means you need to be aware of resisting failure.
Resisting failure can manifest itself very subtly, but the most common manifestation for me is resisting something because it involves new learning ("I just want to solve the core problem, this is never going to end!"), or doing something that I "know" I won't be as good as others at e.g. the user interface.
It's obviously better to get something working than not, and knowing this keeps me committed to working in principle. So I don't abandon the project outright. What actually happens is more insidious: I do something else to avoid the pain of dealing with the problem at hand. As time passes, I (a) lose momentum on the project and (b) the likelihood of a bright, new shiny idea occurring to me, with challenges I "know" I can solve, increases.
When (b) happens, I move on, and it feels good because I'm making progress whereas with the other project I "couldn't" make progress. I never specifically or intentionally abandon the original project, but in effect I do, with the rationalisation that I have a higher priority item to focus on i.e. something I believe I can 'make progress' on. At least, as it turns out, according to my dysfunctional definition of progress, which is rooted in perfectionism.
What I've learned is to monitor my objective progress: did I take steps to solve the problem, and can I solve it for the bulk of the use cases that are really important, and if not can I find somebody else to solve it? e.g. do I have a user interface yet or not, and do I need to find somebody to do it for me? Not my subjective progress: e.g. "I really want this to look great and professional like all those other sites out there, and I'll never get there because I don't know how and I don't want to blow money on this because I'm not even sure how I want it to look, maybe I should research more and find something similar, this is boring it's not what I want to do, I'm making no progress, etc."