They're in a room with juveniles and with no adult to call their bullshit.
Back in the day when teachers worked for peanuts they had to do work summer jobs. They got their chops busted when necessary and learned some humility.
Exception to this, today, are coaches, who work in a public setting and are subject to criticism from other adults. Former coaches make the best school administrators, in my experience. They view conflict differently. It's part of the picture and requires one to grow beyond a satisfaction with mediocre performance. Also, you shake hands afterwards, the other guys are still your friends, and you concentrate on the next game (problem).