Become curious about how much stronger practice can make you.

Approaching your own development as a question rather than a verdict changes what you are willing to attempt. Wondering how far practice could take you is open ended and keeps you experimenting, whereas deciding in advance what you are capable of closes the matter and makes further effort seem pointless. The curiosity is not optimism, it is simply leaving the question open.

Pick something you have never seriously practised and treat it as an experiment rather than a test of your worth. Give it a fixed period and see what happens. The result is genuinely unknown, which is the interesting part.