Generally speaking, punishment makes men hard and cold; it concentrates; it sharpens the feeling of alienation; it strengthens the power of resistance. Friedrich Nietzsche
Math is like going to the gym for your brain. It sharpens your mind. Danica McKellar
Meditation is all about the pursuit of nothingness. It's like the ultimate rest. It's better than the best sleep you've ever had. It's a quieting of the mind. It sharpens everything, especially your appreciation of your surroundings. It keeps life fresh. Hugh Jackman
You would advise us not to worry?” "Oh, worry by all means,” said Windlow. "By all means. Yes. It sharpens the wits. A good worry does wonders for the defensive capabilities of the brain. However, I should not advise you to do without sleep. Sheri S. Tepper
Sorrow may sadden your face but it sharpens your understanding. African Proverb