‘Try to attend steadfastly to a dot on the paper or on the wall. You presently find that one or the other of two things has happened: either your field of vision has become blurred, so that you now see nothing distinct at all, or else you have involuntarily ceased to look at the dot in question, and are looking at something else. But, if you ask yourself successive questions about the dot,—how big it is, how far, of what shape, what shade of color, etc.; in other words, if you turn it over, if you think of it in various ways, and along with various kinds of associates,—you can keep your mind on it for a comparatively long time. This is what the genius does, in whose hands a given topic coruscates and grows.’
William James, ‘Attention’, Talks to Teachers.