Seek natural limits. Seneca, Epistles 4.39.5-6

What is moral depravity? Seneca argues that it is lacking natural limits for our desires. Without natural limits, we want things that are too much, too large, too unbalanced to be good for us. Over time, having too much will manifest as a permanent shift in our habits and character that causes us to want excess as a rule, as though it were good and necessary (i.e. virtuous), though it is not. Philosophy should teach us to want only what is needed, naturally, not what is excessive, though it appear desirable.

Qui hostis in quemquam tam contumeliosus fuit quam in quosdam voluptates suae sunt? quorum impotentiae atque insanae libidini ob hoc unum possis ignoscere, quod quae fecere patiuntur. Nec immerito hic illos furor vexat; necesse est enim in immensum exeat cupiditas quae naturalem modum transilit. Ille enim habet suum finem, inania et ex libidine orta sine termino sunt. Necessaria metitur utilitas: supervacua quo redigis? Voluptatibus itaque se mergunt quibus in consuetudinem adductis carere non possunt, et ob hoc miserrimi sunt, quod eo pervenerunt ut illis quae supervacua fuerant facta sint necessaria. Serviunt itaque voluptatibus, non fruuntur, et mala sua, quod malorum ultimum est, et amant; tunc autem est consummata infelicitas, ubi turpia non solum delectant sed etiam placent, et desinit esse remedio locus ubi quae fuerant vitia mores sunt. Vale.

What enemy has ever treated a man as cruelly as his own pleasures will, given the chance? Only one way to remain indifferent here to the impotence and insane lust of so many that have succumbed: remember that they caused their own suffering. The madness that shakes them is but their due, for it is inevitable that desire should go forth to great ruin once it has escaped the rhythm of nature. That rhythm carries its own end, but the empty desires that rise from unbridled lust are without bounds. Immediate need or use measures things that we require. But how do you keep needless things in check? With no good answer to this question, people drown themselves in pleasures that turn into habits they cannot live without, and they become utterly miserable for this one reason, that they must regard what is useless as though it were entirely necessary. So they become enslaved to pleasures, rather than enjoy them, and love their own evil, the worst outcome possible. This is the consummation of their misery, that what is awful does not merely delight or amuse them: it pleases them, genuinely, and their character loses any room for improvement, since what were originally vices have become its virtues. Farewell.