Ego is one of the reasons why I avoid hiking in a large group nowadays. Especially with people I don't know personally. On longer, more demanding treks there's bound to be some conflicts in a large group. We're all different: some are in a better shape than others, some love to hike fast and some prefer a slower pace, some like to talk all the time and others don't... and some people just can't get along no matter what. Heat, cold, difficult weather, lack of sleep, having had a few beers too many - all the little factors that can turn a nice trek into a not so pleasant experience.

A little competition on the trail might still be ok but if someone's ego is too big the potential for disaster increases rapidly. I'm in a pretty good shape and don't mind pushing myself hard now and then, but you have to understand full well just how far you can push yourself and how much your buddies can take. If your hiking trip turns into a death march it's only a question of time before somebody gets injured and at any rate the group cohesion will suffer because some people won't be able to keep up the pace.