John Cassian, The Institutes IX.6: That no one comes to grief by a sudden fall, but is destroyed by falling through a long course of carelessness

That no one comes to grief by a sudden fall, but is destroyed by falling through a long course of carelessness.

For no one is ever driven to sin by being provoked through another’s fault, unless he has the fuel of evil stored up in his own heart. Nor should we imagine that a man has been deceived suddenly when he has looked on a woman and fallen into the abyss of shameful lust: but rather that, owing to the opportunity of looking on her, the symptoms of disease which were hidden and concealed in his inmost soul have been brought to the surface.