Letters 85.9

Again, if reason prevails, the passions will not even get a start; but if they get under way against the will of reason, they will maintain themselves against the will of reason. For it is easier to stop them in the beginning than to control them when they gather force. This half-way ground is accordingly misleading and useless; it is to be regarded just as the declaration that we ought to be “moderately” insane, or “moderately” ill.

Seneca, Letters to Lucilius 85.9, translated by Richard Mott Gummere