Great description of burnout: "What I learned is that burning out isn’t just about work load, it’s about work load being greater than the motivation to do work."
This is the reason you see musicians take 5 year breaks, or even quitting music. They are lacking in motivation. Look at the band Queen, They are still making music and touring, but half the band has quit. Freddie Mercury died and John Deacon quit music altogether. What did John Deacon lose? His motivation. Brian May and Roger Taylor both had a lot of say in the bands creative process, and that process motivated them to continue, even after Freddie had passed away. Now, Deacon, he wasn't as involved in that process, and he was the one who quit.
Advantages of doing http://c2.com/cgi/wiki?PairProgramming
That may not have been true at the time the gp indicates though.
John Deacon had a very small part in their total creative output, and so, his contributions to their creative development wasn't comparable to that of the other members.
I always wondered what caused people to 'burn out' on jobs that you couldn't possibly call taxing by any stretch of the imagination, I think this is the key to the answer.