Altogether it will be found that a quiet life is characteristic of great men, and that their pleasures have not been of the sort that would look exciting to the outward eye. No great achievement is possible without persistent work, so absorbing and so difficult that little energy is left over for the more strenuous kinds of amusement, except such as serve to recuperate physical energy during holidays, of which Alpine climbing may serve as the best example..
Source:The Conquest of Happiness, 1930, chap.4：Boredom and Excitement
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