10 But in order that we fall not away from Continence, we ought to watch specially against those snares of the suggestions of the devil, that we presume not of our own strength. For, “Cursed is every one that sets his hope in man.” And who is he, but man? We cannot therefore truly say that he sets not his hope in man, who sets it in himself. For this also, to “live after man,” what is it but to “live after the flesh?” Whoso therefore is tempted by such a suggestion, let him hear, and, if he have any Christian feeling, let him tremble. Let him hear, I say, “If you shall live after the flesh, you shall die.”
Source: On Continence (New Advent)