Diogenes Laërtius

Time is the most valuable thing that a man can spend.

One original thought is worth a thousand mindless quotings.

We have two ears and only one tongue in order that we may hear more and speak less.

We are more curious about the meaning of dreams than about things we see when awake.

Step out of my sunlight.

One day a man invited him into a richly furnished house, saying 'be careful not to spit on the floor.' Diogenes, who needed to spit, spat in his face, exclaiming that it was the only dirty place he could find where spitting was permitted.

As to the gods, I have no means of knowing either that they exist or do not exist. For many are the obstacles that impede knowledge, both the obscurity of the question and the shortness of human life.

Why not whip the teacher when the student misbehaves?