No two minds are alike, [just as] no two faces are alike.

Berachot 58a

Even from a foe a man may learn wisdom.

Greek proverb

It's not enough to learn how to ride, you must also learn how to fall.

Mexican Proverb

Zeal without knowledge is fire without light.

Thomas Huxley

What's done is done.

Hilliard MacBeth

I'm not young enough to know everything.

J.M. Barrie