Mental diseases grow just like philosophers say they do. Say you want money. If you use reason to see how bad this desire is, the wanting stops. Your mind gets back its proper control. But if you don't treat it, your mind doesn't return to its healthy state. The next time something triggers that desire, it flares up faster and stronger than before. When this keeps happening, the desire hardens into a permanent craving. The disease of greed takes hold. Think of someone who had a fever and recovered. They're not the same as before unless they were completely healed. The same thing happens with diseases of the soul. Certain marks and tender spots remain. If you don't completely erase them, the next time you get hit in those same places, you won't just get welts — you'll get open wounds.
In this manner certainly, as philosophers say, also diseases of the mind grow up. For when you have once desired money, if reason be applied to lead to a perception of the evil, the desire is stopped, and the ruling faculty of our mind is restored to the original authority. But if you apply no means of cure, it no longer returns to the same state, but being again excited by the corresponding appearance, it is inflamed to desire quicker than before: and when this takes place continually, it is henceforth hardened (made callous), and the disease of the mind confirms the love of money. For he who has had a fever, and has been relieved from it, is not in the same state that he was before, unless he has been completely cured. Something of the kind happens also in diseases of the soul. Certain traces and blisters are left in it, and unless a man shall completely efface them, when he is again lashed on the same places, the lash will produce not blisters (weals) but sores.