What is wrong about stress?
The hippocampus is especially vulnerable to ongoing emotional distress, because of the damaging effects of cortisol. Under prolonged stress, cortisol attacks the neurons of the hippocampus, slowing the rate at which neurons are added or even reducing the total number, with a disastrous impact on learning.
Many effective leaders sense that - like compliments - well-titrated doses of irritation can energize. The measure of how well calibrated a message of displeasure might be is whether it moves people toward their performance peak or plummets them past the tipping point into the zone where distress corrodes performance.
--Daniel Goleman