There's this awkward thing that happens to all musicians at some point. They get good enough that it becomes difficult to play anything at all.
As your skill increases, so do your standards. So everything you play feels mediocre. The weirdest part is that this "mediocre" performance is better than anything you were doing before. You've just moved the goalposts as you improved.
1/
You have to give yourself permission to suck. To play even if you think it's bad. What's going to happen is either:
A) You end up surprising yourself by how well you actually can perform when you push yourself
OR
B) You play something that has issues but those issues are easily improved with a little practice later on, bringing the performance up to something that meets your standards.
2/
You have to be willing to ignore that emotional reflex of "wow this sucks, I suck" and do the thing anyway.
And NO, this doesn't just apply to musicians. This happens with every single kind of artist and craftsperson. Most people tend to quit just when they're starting to get good, because learning to do the thing is the same skill as learning to correctly appraise your skill. (This is called the Dunning-Kreuger effect, by the way.)
3/
Don't quit just because your standards have raised along with your skill!
I find myself wondering sometimes how many musicians have reached this phase, believe wrongly that they suck, and never pick up their instrument again -- JUST at the exact moment they're really getting good!
I'd imagine quite a lot of them.
4/4
I try and encourage people to keep old versions or attempts at projects, so that in say 12 months time when they have made improvements they can look back and see how they have developed over time.