For things like applying for better paying jobs, coding open source software (and not being concerned your code sucks), writing articles, building your own commerical products, building a business network, doing freelance work, etcetera.
I always feel like I'm not good enough or worse that I'll never be good enough. I've done things in those area's that I'm proud of but I still feel this gnawing anxiety that I won't ever be good enough. This applies to everything outside the scope of this question as well.
I won't apply for jobs that I think I'm not good enough for, I don't want to publish any of my projects code because I fear its trash and people will be critical of it. I like to write but I don't feel confident about what I can contribute.
To me the anxiety of not feeling like I'll ever be good enough sucks all the joy out of these things. I've stopped projects that once inspired me and never returned. I'm not even sure why. I just get this anxious feeling that only goes away when I give up and distract myself with entertainment.
Look for objective feedback and praise you've received from other people. Most people give compliments when they mean it honestly. Depending on the situation, you can take people's word for it.
Think about how you've gotten better. Do you think back to anything you did in the past and feel like you'd do it better now? That means you've learned.
Things like that are not delusional and giving yourself credit for that is not bullshit.
I suspect with both of us that these feelings touch on something deeper that just reflecting on past progress may not fully address. I'm still struggling with it.
Have you seen a therapist before? These are the kinds of things they're good at dealing with.