Nature has limits. Seneca, Epistles 2.16.7-9

Natural desires carry limits: it is very hard to eat too many apples. Unnatural desires have no limit: it is very easy to want too much money.

Iam ab initio, si te bene novi, circumspicies quid haec epistula munusculi attulerit: excute illam, et invenies. Non est quod mireris animum meum: adhuc de alieno liberalis sum. Quare autem alienum dixi? quidquid bene dictum est ab ullo meum est. Istuc quoque ab Epicuro dictum est: si ad naturam vives, numquam eris pauper; si ad opiniones, numquam eris dives. Exiguum natura desiderat, opinio immensum. Congeratur in te quidquid multi locupletes possederant; ultra privatum pecuniae modum fortuna te provehat, auro tegat, purpura vestiat, eo deliciarum opumque perducat ut terram marmoribus abscondas; non tantum habere tibi liceat sed calcare divitias; accedant statuae et picturae et quidquid ars ulla luxuriae elaboravit: maiora cupere ab his disces.

Naturalia desideria finita sunt: ex falsa opinione nascentia ubi desinant non habent; nullus enim terminus falso est. Viam eunti aliquid extremum est: error immensus est. Retrahe ergo te a vanis, et cum voles scire quod petes, utrum naturalem habeat an caecam cupiditatem, considera num possit alicubi consistere: si longe progresso semper aliquid longius restat, scito id naturale non esse. Vale.

If I know you well, you'll be looking now to see what little gift this epistle has brought you. Shake it, and you'll see! No need to marvel at my mind, as my generosity to date has brought you the words of others, strange to my mouth. But why call them strange? Whatever is well said is mine, though another utter it. Here is yet another saying from Epicurus, then: "If you live according to nature, you will never be poor; but if you live by human expectations, you will never be rich." Nature desires only the bare minimum; expectation has no limit. Suppose you manage to accumulate a pile of whatever it is that rich folk have possessed. Fortune would drive you to exceed the bounds of your personal style—covering your home with gold, clothing you in purple, making you such a fan of luxury and opulence that you begin hiding the good earth with marble. It would not be enough then to have riches: you would need to wallow in them. Statues would attack you, and pictures, and all the offerings every art makes to luxury. From them you will only learn to want more.

Natural desires have limits. Desires born of false expectation do not: they extend everywhere, in all directions, with no boundary at all. The traveler who takes a path finds something at the end of it. Aimless wandering has no end. Hold yourself back, then, from chasing every impulse, and when you want to know what one of them prompts you to seek, whether it holds a natural desire or one that is blind, consider if it can stop anywhere. If it shows you always something further to achieve, no matter how far you have come, know then that it is not natural. Farewell.