During my time running music workshops in prison I've come across some extraordinarily talented men. If you get locked up with a guitar for most of the day for a few years I think you could expect to get quite good.
I've also come across guys who have the potential to become extremely talented but whose attitudes are starting to stifle / have stifled their gifting slightly.
I've also seen those who probably will never be musically brilliant but seem to think that their drumming ability is in the same league as John Bonham or that they can nail guitar solos like Jimi Hendrix.
The first kind generally have the following in common: They lap up correction and advice. They watch like hawks for different and new techniques. They are self-correcting. They listen to themselves and are always picking out flaws, never really satisfied. The sky is the limit with this type of musician.
The second kind have the following in common: They don't listen all the time. They interrupt. They don't think they need to heed the whole advice and correction. They often start attempting to play something before you've finished playing it to them. They listen to themselves and are generally happy with how they're playing and content to leave things as they are. Above average. They can slip backwards towards the third kind.
The third kind have the following in common: They listened at first. They had to in order to get playing. Somewhere along the road they decided that they knew best. They don't listen anymore. Not to others, not to themselves. Any correction is seen as an attack on their character. They play the same stuff over and over again, overconfidently and sloppily. These guys drive everyone else in the room with them MAD. They get kicked out of the band.
As a guy who falls into the 2nd category (and slipping back into the 3rd category) said to me as I tried to teach him a part after 3 or 4 failed attempts to play a song correctly (alongside a cocky unwillingness to play without chords in front of him),
“Don't worry, I'll pick it up. I play by ear, I do.”
Me - “mmm, kind of...”
Are you still listening?
Shut up and listen.