…Constant fasting withers lust and begets patient endurance, endurance courage, courage stillness, stillness prayer, prayer silence, silence inward grief, and grief begets humility. Or, going in the reverse order, you will find how daughters give birth to mothers–how, that is to say, humility begets inward grief, and so on. In the realm of the virtues there is nothing more important than this form of mutual generation. The things opposite to these virtues are obvious to all.
St Gregory of Sinai (Philokalia, vol.4, p.272)