A story of an old man who fell because he lacked the virtue of discretion.
Some definite examples may help to reinforce this, so I remind you of a certain old man called Heron, who by paying no attention to discretion brought to nothing all his earlier labours and, what is more, came to a miserable end. A few days ago by the tricks of the devil he was cast down from the heights to the very depths. For he had spent fifty years in the desert, maintaining an extremely strict way of life, preserving the hiddenness of solitude more than anyone else. He worked so very hard, and yet he has been deceived by the deceiver, coming to disaster by such a grievous fall that he has plunged all the desert-dwellers into the deepest grief. He would have run much less risk of falling if he had only practised the wisdom of discretion. Instead, he always practised fasting with such a rigorous spirit and kept so immutably to the hidden solitude of his cell that he would not even relax his strict abstinence on Easter Day. For such a great feast as Easter all the hermits would come together in church, all except him alone, lest he should be seen to have relaxed his rule simply by taking a little extra food.
Such presumption led him into mistaking the angel of Satan for an Angel of light, whom he welcomed with the deepest veneration. He obeyed the angel’s commands and cast himself headlong into a very deep well, thinking that he was about to demonstrate how greatly his virtues were going to be rewarded by coming out of the well unharmed. The brothers with great difficulty managed to get him out of the well half dead, but he died three days afterwards. And what was even worse, he persisted obstinately in his delusions, and no one could convince him that he had been led astray by the devil.
De Vitis Patrum, Book IV, Chapter 43 (Cassian, Conference 2, chap.5)