[CapnJim]

A lot of it is just fear, and the weaker instructors, being ashamed of thier fear, convert it into agression, and direct that agression at the closest person: the student. You'll notice a lot of the excuses for bad behavior rooted in fear, as in, "He was trying to kill me" or "I'm not ruining my career for you!!"
It's all a euphemism for 'lack of intestinal fortitude' or, more colloqially, "not keeping your sh't together". Here's an example of ehat I mean: Armstrong lands on the moon. First words he says? "After landing checklist" (see B767's sticky in General Topics). Pretty f'n cool.
To a *infinitely* lesser degree, I had a student spin me at 2000 agl, full power, full flaps, and then froze on the controls. I said "My aircraft. My aircraft." The second time more sternly, when I realized he was frozen. No freaking out, no hitting the guy. The next thing I said was "Hey, what say we go do some pattern work for a while?"
Now, I'm not some ice-in-his veins superpilot cheeseball, I just knew that calm always trumps panic, and if I freaked out in proportion to how I felt that kid would never fly again. He passed his checkride. He's fine.
Guess what: they're always trying to kill you. If you can be cool regardless, then you can be cool anywhere, and you're the guy I want to strap into a jet with.