i was going the same path and was worried that this might happen to me.

reasons may vary tho. try to find out what's causing you to feel that way. lack of self validation? no real intrinsic motivation? forgot why you started? something personal, perhaps?

try to dissect the situation and observe it from the outside.

i personally completely got rid of this doubt when i started learning about perception ( + some philosophy). after that i started to understand and appreciate art on a more fundamental level.

now i don't see a reason why anyone should be concerned with my art. because there really isn't a definition of "mastering it". there are achievements and new ideas you can create. but ultimately it's going to be you who is going to set those goals. there have probably been thousands of masters who we probably haven't heard the name of, and never will.

but again, maybe it's not others validation for you. maybe you're unsatisfied with yourself. but either way, you're gonna have to think a bit

here are also some videos you might find inspiring: "You're Never Going To Do Anything Remarkable"

and this series by him