I noticed that I have missed to give a more elaborate in-depth explanation why I think learning how to play an instrument a song¹ and I think that might not be obvious so let me explain.²

Rehearsing the same part 1000 times is a lot better than to have a great setup. You don't need a great app which automatically scrolls the piano sheet for you, great lighting or the best music-stool to "git gud".

I suck at not obsessing over mistakes so I will force myself to just continue playing if I made a single (or a few) mistakes. I used to have a guitar teacher, he told me this and I still learn every day a little bit more how true it is:

I also tend to play faster than I should when I don't know what I am doing. I think it's because I immediately want to recognize the song and thus play it in the same speed. But the skill is to realize that you're not ready yet and play intentionally slower than your max speed. You need to find your own weak speed.

Surround yourself with your own failures by recording yourself during a practice session. Don't only record yourself when you think you can play the full song with zero mistakes now. You need to record your failures. If you do this, you'll quickly see that your latest failure is less of a failure than the failure before.

Don't play easy songs all the time. Play the songs think you can't play yet because it's too fast, seems to require four hands or has too many weird notations that you've never seen.