I worked line for a 135 King Air/Lear outfit when I was 19. After that, I was a bag smasher for American. At the time I thought, "sure wish I was in the cockpit of a jet and not down here smashing bags". Lo and behold, I did 6 years at a frac and I was in the cockpit AND smashing bags! Anyway, done with handling bags.

I realize that it is impractical that every pilot do it. However, if possible, an aspiring pilot should work as a lineman just like aspiring automotive/aerospace engineers should be automotive/aircraft mechanics first. It really helps with one's perspective.