Those who know, do. Those that understand, teach.

Teaching is the highest form of understanding.

It is Homer who has chiefly taught other poets the art of telling lies skillfully

To perceive is to suffer.

Strange that the vanity which accompanies beauty - excusable, perhaps, when there is such great beauty, or at any rate understandable -should persist after the beauty was gone.

The one exclusive sign of thorough knowledge is the power of teaching.