"The basic disease is sloth. It is that strange laziness and passivity of our entire being which always pushes us 'down' rather than 'up'--which constantly convinces us that no change is possible, and therefore desirable. It is in fact a deeply rooted cynicism which to every challenge responds 'what for?' and makes our life one tremendous spiritual waste. It is the root of all sin because it poisons the spiritual energy at its vital source.
The result of sloth is faint-heartedness. It is the state of despondency which all spiritual fathers considered the greatest danger for the soul. Despondency is the impossibility for man to see anything good or positive; it is the reduction of everything to negativism and pessimism. It is truly a demonic power in us because the Devil is fundamentally a liar. He lies to man about God and about the world; he fills life with darkness and negation. Despondency is the suicide of the soul because when man is possessed by it he is absolutely unable to see the light and to desire it."
Alexander Schmemann, Great Lent (2003), 34-35.