Epictetus has a wonderful quote. He is talking about moral / philosophical improvement specifically but I find it more broadly applicable when overly high expectations paralyse me from doing a thing:
"What then? Because I have no natural gifts, shall I on that account give up my discipline? Far be it from me! Epictetus will not be better than Socrates; but if only I am not worse, that suffices me. For I shall not be a Milo, either, and yet I do not neglect my body; nor a Croesus, and yet I do not neglect my property; nor, in a word, is there any other field in which we give up the appropriate discipline merely from despair of attaining the highest."
"What then? Because I have no natural gifts, shall I on that account give up my discipline? Far be it from me! Epictetus will not be better than Socrates; but if only I am not worse, that suffices me. For I shall not be a Milo, either, and yet I do not neglect my body; nor a Croesus, and yet I do not neglect my property; nor, in a word, is there any other field in which we give up the appropriate discipline merely from despair of attaining the highest."