When two friends part they should lock up each other's secrets and exchange keys. The truly noble mind has no resentments.
The sun, too, shines into cesspools and is not polluted.
If you are to be kept right, you must possess either good friends or red-hot enemies. The one will warn you, the other will expose you.
There is only a finger's difference between a wise man and a fool.
Nothing can be produced out of nothing.
Democritus says, "But we know nothing really; for truth lies deep down".