Most people want to avoid pain, and discipline is usually painful.
To measure a leader, put a tape around his heart, not his head.
It's said that a wise person learns from his mistakes. A wiser one learns from others' mistakes. But the wisest person of all learns from others's successes.
A person who refuses to risk change fails to grow.
Praise them for what they do well, both privately and publicly.
If you are training leaders, because you need them, you are too late.