"To teach effectively a teacher must develop a feeling for his subject; he cannot make his students sense its vitality if he does not sense it himself. He cannot share his enthusiasm when he has no enthusiasm to share. How he makes his point may be as important as the point he makes; he must personally feel it to be important."
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Source : George Pólya, Leon Bowden (1977). “Mathematical Methods in Science”, p.1, Cambridge University Press