Men can be brilliant and strong, they whispered to one another. But men can be mad, as well. And the mad ones can ruin the world. - David Brin

He tried again, but their sullen, rural obstinacy was impervious to logic.

Master, I marvel how the fishes live in the sea.” “Why, as men do aland — the great ones eat up the little ones.” — WILLIAM SHAKESPEARE King Richard the Second

It's said that 'power corrupts,' but actually it's more true that power attracts the corruptible. The sane are usually attracted by other things than power. When they do act, they think of it as service, which has limits. The tyrant, though, seeks mastery, for which he is insatiable, implacable.