From The Meditations

when you do become angry, be ready to apply this thought, that to fly into a passion is not a sign of manliness, but rather, to be kind and gentle. For as these qualities are more human, they are also more manly. It is the man who possesses such virtues who has strength, nerve, and fortitude, and not one who is ill-humoured and discontented. Indeed, the nearer a man comes in his mind to freedom from unhealthy passions , the nearer he comes to strength. Just as grief is a mark of weakness, so is anger too, for those who yield to either have been wounded and have surrendered to the enemy