When brothers agree, no fortress is so strong as their common life.
There are only two people who can tell you the truth about yourself - an enemy who has lost his temper and a friend who loves you dearly.
The most useful piece of learning for the uses of life is to unlearn what is untrue.
Pay attention to your enemies, for they are the first to discover your mistakes.
We weed out the darnel from the corn and the unfit in war, but do not excuse evil men from the service of the state.
Not to unlearn what you have learned is the most necessary kind of learning.