Wisdom is an art

That which takes effect by chance is not an art. Now wisdom is an art; it should have a definite aim, choosing only those who will make progress, but withdrawing from those whom it has come to regard as hopeless—yet not abandoning them too soon, and just when the case is becoming hopeless trying drastic remedies.

Seneca, Epistulae Morales ad Lucilium, XXIX. ON THE CRITICAL CONDITION OF MARCELLINUS