Letters 85.11

Again, if you grant any privileges to sadness, fear, desire, and all the other wrong impulses, they will cease to lie within our jurisdiction. And why? Simply because the means of arousing them lie outside our own power. They will accordingly increase in proportion as the causes by which they are stirred up are greater or less. Fear will grow to greater proportions, if that which causes the terror is seen to be of greater magnitude or in closer proximity; and desire will grow keener in proportion as the hope of a greater gain has summoned it to action.

Seneca, Letters to Lucilius 85.11, translated by Richard Mott Gummere