Whoever wants to know a thing has no way of doing so except by coming into contact with it, that is, by living (practicing) in its environment… If you want knowledge, you must take part in the practice of changing reality. If you want to know the taste of a pear, you must change the pear by eating it yourself… If you want to know the theory and methods of revolution, you must take part in revolution. All genuine knowledge originates in direct experience.
Mao Tse Tung “On Practice” (July 1937), Selected Works, Vol. I, pp. 299-300.