Letters 94.30

Or, if precepts do not avail at all, then every method of instruction should be abolished, and we should be content with Nature alone.

Those who maintain this view do not understand that one man is lively and alert of wit, another sluggish and dull, while certainly some men have more intelligence than others. The strength of the wit is nourished and kept growing by precepts; it adds new points of view to those which are inborn and corrects depraved ideas.

Seneca, Letters to Lucilius 94.30, translated by Richard Mott Gummere