Anger and emotion are strategically counterproductive. You must always stay calm and objective. But if you can make your enemies angry while staying calm yourself, you gain a decided advantage. Put your enemies off-balance. Find the chink in their vanity through which you can rattle them and you hold the strings. –Robert Greene, The 48 Laws of Power (review)
He who is slow to anger has great understanding,
But he who is quick-tempered exalts folly.
He who is slow to anger is better than the mighty,
And he who rules his spirit, than he who captures a city.