Not to unlearn what you have learned is the most necessary kind of learning.

As rust corrupts iron, so envy corrupts man.

The most necessary learning is that which unlearns evil.

Not to unlearn what you have learned is the most necessary kind of learning.

I am sadly afraid that I must have done some wicked thing.

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.

We must not contradict, but instruct him that contradicts us; for a madman is not cured by another running mad also.