“I am indeed, a king, because I know how to rule myself.” Pietro Aretino
Whomever can subjugate their desires to their will, that can sacrifice current pleasure for future greatness, is worthy to lead.
Those who rule their passions can rule others.
Those who have discipline can wield power responsibly and thus should, because they know that with great power comes great responsibility. Self restraint keeps their sword sheathed and their tongue from wagging.
Self-command is the first criteria to be able to command others.