2 “Reproof,” Diogenes was wont to say, “is another's blessing.”
3 One of the youths who were disciplines of Diogenes, when questioned by him, remained silent. But Diogenes remarked, “Do you not believe that it is to be expected of the same man that he should know, not only what he should say and when, but also what he should refrain from saying and before whom?”
Source: Discourses by Dio Chrysostom published in the Loeb Classical Library, 1932. The text is in the public domain.