The use of self-control is like the use of brakes on a train. It is useful when you find yourself going in 'the wrong direction, but merely harmful when the direction is right. No one would maintain that a train ought always to be run with the brakes on, yet the habit of difficult self-control has a very similar injurious effect upon the energies available for useful activity.
Source：Marriage and Morals, 1929, chap. 21: Conclusion.
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