I think being laid back and a bass player tend to go hand in hand. To be good at bass, you have to accept that you aren't the center of attention all the time, and that's difficult if you can't relax and accept your importance in the music. And I feel like bassists also usually know theory the most (Steve Harris writes the majority of Iron Maiden's songs, Cliff Burton taught Metallica kind of everything). I told my guitarist once how to play a harmony part, after pointing out every fret, and he got confused. So I told him to think in the G major scale shape, and it confused him more.