Letters 40.13

However, I have this further reason for frightening you away from the latter malady, namely, that you could only be successful in practising this style by losing your sense of modesty; you would have to rub all shame from your countenance, and refuse to hear yourself speak. For that heedless flow will carry with it many expressions which you would wish to criticize.

Seneca, Letters to Lucilius 40.13, translated by Richard Mott Gummere