Letters 66.8

Whatever it has touched it brings into likeness with itself, and dyes with its own colour. It adorns our actions, our friendships, and sometimes entire households which it has entered and set in order. Whatever it has handled it forthwith makes lovable, notable, admirable.

Therefore the power and the greatness of virtue cannot rise to greater heights, because increase is denied to that which is superlatively great. You will find nothing straighter than the straight, nothing truer than the truth, and nothing more temperate than that which is temperate.

Seneca, Letters to Lucilius 66.8, translated by Richard Mott Gummere