Good question. I think you need to firstly consider what you mean by good. Would more studying, practice make you better? If so, try and do this. If you want to be more pragmatic maybe think if there is something that you might be better at and think about pursuing it. Although I would recommend doing something that you love because of the motivation and interest that comes with that love meaning that you will put in more effort and probably achieve great results. But of course there are other things to consider like making a living but I am not sure if this is what is being asked. Good luck!
It depends on how it makes you feel. Do you feel inferior? agitated? restless & stressed out with yourself for not being able to excel at what you love to do? Or do you have moments where you think to yourself, "you know what, i could do this forever. I could slowly build confidence and improve over time." How does being bad at your job, effect you as a person, essentially? and is it worth it?
I love karaoke but I am definitely no Beyoncé. Keep doing what you love! However, if this is something (e.g. you’re a doctor who has a fear of blood) that is having a significant impact on yours or someone else’s life then maybe it’s something that you have to love and let go and realise it’s for the greater benefit. But usually if you have a recognisable passion for what you’re doing, then the likelihood is that you are good at what’s you love - your anxiety is just holding you back from your full potential. If this is the case, start to believe in yourself!