This was years ago. I flew to Arizona for work, and my friend Patrick picked me up. We proceeded to a music store to jam on their equipment, as we had nothing better to do. We were jammin' blues, and somone is one row of amps over, playing some note-perfect Rush. It's like Alex Lifeson himself was playing "YYZ". Actually, I don't think it was "YYZ", but we'll pretend it was so we can go onto the next step.
Which is us, awestruck at this guy's playing, inviting him to play with us.
We played "Bog-Standard Blues Shuffle in A".
He fell off.
It befuddled me then. It befuddles me now.
If there's anything fundamental to rock, it's the 12-bar blues. If you're going to play rock with someone else, eventually you're going to have to find common ground, and the common ground for musicians has been the 12-bar for at least 80 years.
Ergo, this fantastic player never had the luxury of playing with anyone else.
There are things you can do to be better that are solitary pursuits, to be sure, and there are plenty of fine guitarists who are entirely solo players. But beyond that, to really get better, you have to play with someone. Because it's then you learn, sometimes painfully, by knowing where you fall off.