OTHER VICES sometimes subside by beneficial surroundings; once opportunity, occasion, or matter of sin are removed, they slow down and diminish; but vanity penetrates the deserts along with the one who flees the external world. For it is animated by no other source than the flowering of virtue in the one it hunts. Whereas all other vices may diminish by mere lapse of time, for this one, length of years is no hindrance. Unless diligence is founded on skillful and prudent discernment, the virtues so diligently accumulated will only serve as greater fuels for vanity.
St. John Cassian, The Institutes, XI, 8.