Not so bad!

[Seeing the good in the bad that happens] we should practice and work on first of all - like the man who threw a stone at his dog but missed and hit his stepmother. "Not so bad!" he said. For it is possible to change what we get out of things that do not go as we wish. Diogenes  was driven into exile: "Not so bad!" - for it was after his banishment that he took up philosophy.

- Plutarch, On Tranquility of Mind.

Hippomachus

They say that the trainer Hippomachus, when an athlete he was training competed in wrestling and everyone who was present applauded, struck the student with his staff. "You did it badly, and not as you should have," he said. "You should have done better. If you had done it artfully they would not have applauded you."

- from Various Histories, Aelian.

When some persons praised a tall fellow with a long reach as having the makings of a fine boxer, the trainer Hippomachus remarked: "Yes, if the crown were hung up and to be got by reaching."

- from Plutarch, On Love of Wealth.

For the stars

"He aimed for the stars, but sometimes he hit England."

- Mort Saul on Werner von Braun

the death of knowledge

"Not ignorance, but ignorance of ignorance, is the death of knowledge." - Alfred North Whitehead

As quoted on the excellent futilitycloset.com