Actions seems to follow feeling, but really actions and feeling go together; and by regulating the action, which is under the more direct control of the will, we can indirectly regulate the feeling, which is not. Thus the sovereign voluntary path to cheerfulness, if our cheerfulness be lost, is to sit up cheerfully and to act and speak as if cheerfulness were already there.
William JamesIf an unusual necessity forces us onward, a surprising thing occurs. The fatigue gets worse up to a certain point, when, gradually or suddenly, it passes away and we are fresher than before!
William James