When I was young I thought I was good the best, no one could beat me. Winning competitions pushed this feeling of superiority, getting musical awards from government, learning from the best pianists in Australia etc. Now I don't think about good or bad because it is a stupid way to think. If I think im good I put my music down, I make my music seem like it can be enslaved and I can whip it and slave drive it anywhere I want. To me thinking you are good makes your music experience pretty feel empty and heartless.
The same applies when you think you are really crap. The idea is not to think at all! Not to say you are good or you are bad but instead say, you are doing! I still get asked by people who find out I can play, Oh are you any good? I always say, I'm probably better than you, but only because I've practiced more, and they will laugh because they don't even play

Someone who plays music rarely will ask you, are you any good? They will simply ask you what can you play and the music itself stands for itself. Some people might think if you play an early Mozart Sonata you are brilliant, some might think you are just starting out at the piano, so who is to say what is good or bad?
Thinking you are too good can damage your progress. I started learning pieces much harder than I should and probably wasted 20-30% of my time doing so. I had to start questioning do I like music just to play harder and harder stuff? What is the point in that?? I got the the stage where I was thinking, man I can play all these damn hard pieces which probably less than 1% of pianists play but who really cares and what does that mean? It is meaningless, it just means you can do it, but so what? You don't study music to play harder and harder pieces, that is just totally useless. You play music so you can play music you enjoy, full stop!
The reality is that since the Baby Boomer generation the world has become extremely competitive. Getting the best, achieveing the highest etc etc. It is sickening. Its not to say that the competitive mind hasn't been here since the beginning of time, but it gets out of hand in the life we live now. Look at all these competitions on TV. urrg, why are we so interested in who wins or whos the best? I use to be so interested in the best but I never knew why, it was more of a selfish desire to get better I guess, an impure way to inspire yourself.