The harm that is attributed to overwork is hardly ever due to that cause, but to some kind of worry or anxiety. The trouble with emotional fatigue is that it interferes with rest. The more tired a man becomes, the more impossible he finds it to stop.One of the symptoms of approaching nervous breakdown is the belief that one's work is terribly important, and that to take a holiday would bring all kinds of disaster.
Source: The Conquest of Happiness, 1930, chap.5: Fatigue<
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