Listlessness–a most difficult passion to overcome–makes the body sluggish. And when the body is sluggish, the soul also grows sluggish. When both have become thoroughly lax, self-indulgence induces a change in the body’s temperament. Self-indulgence incites the appetite, appetite gives rise to pernicious desire, desire to the spirit of revolt, revolt to dormant recollections, recollection to imaginings, imagining to mental provocation, provocation to coupling with the thought provoked, and coupling to assent. Such assent to a diabolic provocation leads to actual sinning, either through the body or in various other ways. Thus we are defeated and thus we lapse.
~St Gregory of Sinai