Something to be studied will not of itself sell well. (This is why no one becomes rich writing mathematical monographs.) Something to be studied will sell well only if it is part of a regime (such as a school curriculum). Only something that takes you by the hand sells well on its own. In particular, this is why ‘sex sells’. This phenomenon is in accordance with the Gorgon Principle. (‘Taking you by the hand’ means doing the initial step for you.)
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