The BPS Digest reports that Self-doubt turns bosses into bullies. If power corrupts, it may not corrupt equally. They describe some small scale experiments from which researchers concluded:

Power holders who do not feel personally competent are more likely than those who feel competent to lash out against other people.

That makes some kind of sense to me, and reminds me of Richard Farson's formula, that responsibility plus helplessness leads to abuse.

The researchers add this slightly depressing suggestion:

Additionally, the finding that self-worth boosts assuage the aggressive tendencies of such power holders implies the effectiveness of a strategy commonly employed by underlings: excessive flattery.

I bet we've all seen that strategy in action and I know I've been guilty of it in the past. It stores up even more trouble for the future.