Letters 94.16

Moreover, the precepts of wisdom should be definite and certain: when things cannot be defined, they are outside the sphere of wisdom; for wisdom knows the proper limits of things.

“We should therefore do away with this department of precepts, because it cannot afford to all what it promises only to a few; wisdom, however, embraces all.

Seneca, Letters to Lucilius 94.16, translated by Richard Mott Gummere