"A man becomes a bottomless abyss; he tries hard to fill this abyss, but he cannot. That is why for his whole life he is in sweat, toil, and great troubles. He busies himself with various things in hopes of finding satisfaction for this craving that consumes him. These things occupy his entire attention, all his time, and the whole of his activity. They are his highest good, to which he has devoted his whole heart. Hence it is clear why a man who sets himself up as the main object of his life can never be within himself. He is always focused on things outside of himself; on the things which were created or devised as a result of his own vanity in order to fill his craving."
- St. Theophan the Recluse, Turning the Heart to God, p.5 (published separately, this is the second part of The Path to Salvation).