Peter Drucker gets this right:
“The young knowledge worker whose job is too small to challenge and test his abilities either leaves or declines rapidly into premature middle-age soured, cynical, unproductive.
Executives everywhere complain that many young men with fire in their bellies turn so soon into burned-out sticks. They have only themselves to blame: they quenched the fire by making the young man’s job too small.”
In other words, you burn people out mainly by giving them too little, not mainly by giving them too much.
If you treat your employees simply as tools — that is, simply as interchangeable parts who are there to do what you tell them rather than to take initiative and ownership of their job — you are are not just being an ineffective manager. You are harming your employees (as all bad management ultimately does).