Letters 103.5

But this very philosophy must never be vaunted by you; for philosophy when employed with insolence and arrogance has been perilous to many. Let her strip off your faults, rather than assist you to decry the faults of others. Let her not hold aloof from the customs of mankind, nor make it her business to condemn whatever she herself does not do. A man may be wise without parade and without arousing enmity. Farewell.

Seneca, Letters to Lucilius 103.5, translated by Richard Mott Gummere