Why is teaching so stressful?

It was when head teacher John Illingworth had to stop himself from hitting a parent that he realised he needed to take some time off.

“She was a bit upset with someone else in the school and I just could not cope with the interaction.”
A head teacher of a Nottingham primary school for 24 years, he went on to have a breakdown at the age of 55.
“It was brought on by an accumulation of stresses. I didn’t see it coming but I suddenly found myself unable to do simple things like make decisions or relate to people.