The fool learns by suffering.

...Perses, hear me out on justice, and take what I have to say to heart; cease thinking of violence. For the son of Kronos, Zeus, has ordained this law to men: that fishes and wild beasts and winged birds should devour one another, since there is no justice in them; but to mankind he gave justice which proves for the best.

Only fools need suffer to learn.

And Zeus will destroy this race of mortal men too, when they, at their birth, have grey hair on their temples.

In front of excellence, the immortal gods have put sweat, and long and steep is the way to it.

So the people will pay the penalty for their kings' presumption, who, by devising evil, turn justice from her path with tortuous speech.

Observe due measure, for right timing is in all things the most important factor.