Adam Smith. An inquiry into the nature and causes of the wealth of Nations (№ 347142)

The superiority of the body not supported by the superiority of the mind, in any period of development of society can give only a small power. A very strong man is one who can force solely for his physical strength to obey him two weak people. But only mental skills can give a very great power. Of course, they represent invisible qualities; they are always controversial and commonly disputed.