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"there is no such thing as voluntary attention sustained for more than a few seconds at a time. What is called sustained voluntary attention is a repetition of successive efforts which bring back the topic to mind. The topic once brought back, if a congenial one, develops . . . .  no one can possibly attend continuously to an object that does not change."

Successful concentration consists, then, in continuous acts of attention given to various details   of the object under consideration. No one can long attend to one idea. In fact an idea lingers but a moment. The succeeding moment brings, at best, only an idea that resembles it. It is not only impossible to hold the attention in one direction, without a break, but it is undesirable to try to do this. No one should be discouraged who finds that the attention shifts from phase to phase of the general trend of consciousness. This is the way of nature. Consciousness lives; it is not a dead affair. In all life there is change. The attainments which eventually come out of the realm   of change are due to a succession of little movements. Unity is won by moving in a general direction. And likewise with the mind, unity or concentration is attained by continually bringing the attention back to the point. One should give no thought to the wanderings of attention, but simply turn the mind once more in the chosen direction.