Letters 117.27

Who does not know that what is yet to be is not a Good, for the very reason that it is yet to be? For that which is good is necessarily helpful. And unless things are in the present, they cannot be helpful; and if a thing is not helpful, it is not a Good; if helpful, it is already. I shall be a wise man some day; and this Good will be mine when I shall be a wise man, but in the meantime it is non-existent. A thing must exist first, then may be of a certain kind.

Seneca, Letters to Lucilius 117.27, translated by Richard Mott Gummere