From the chapter on habit, here's James on the importance of developing productive habits early on:
We all intend when young to be all that may become a man before the destroyer cuts us down. We wish and expect to enjoy poetry always, to grow more and more intelligent about pictures and music...We mean all this in youth, I say; and yet in how many middle-aged men and women is such an honest and sanguine expectation fulfilled? Surely, in comparatively few, and the laws of habit show us why. Some interest in each of these things arises in everybody at the proper age, but if not persistently fed with the appropriate matter, instead of growing into a powerful and necessary habit, it atrophies and dies, choked by the rival interests to which the daily food is given.Or, more pithily, are you going to be an interesting middle-aged person or are you going to be someone whose tastes are frozen in time at age 22?
We say abstractly: "I mean to enjoy poetry, and to absorb a lot of it, of course. I fully intend to keep up my love of music, to read the books that shall give new turns to the thought of my time..." But we do not attack these things concretely, and we do not begin today. We forget that every good that is worth possessing must be paid for in strokes of daily effort. We postpone and postpone, until those smiling possibilities are dead. Whereas ten minutes a day of poetry...and an hour or two a week at music, pictures, or philosophy, provided we began now and suffered no remission, would infallibly give us in due time the fulness of all we desire. By neglecting the necessary concrete labor, by sparing ourselves the little daily tax, we are positively digging the graves of our higher possibilities.
In the chapter on attention, James also has some helpful comments on what we would, these days, call learning disabilities:
But I wish to make a remark here which I shall have occasion to make again in other connections. It is that no one need deplore unduly the inferiority in himself of any one elementary faculty. This concentrated type of attention is an elementary faculty; it is one of the things that might be ascertained and measured by exercises in the laboratory. But having ascertained it in a number of persons, we could never rank them in a scale of actual and practical mental efficiency based on its degrees. The total mental efficiency of a man is the resultant of the working together of all his faculties; he is too complex a being for any one of them to have the casting vote. If any one of them do have the casting vote, it is more likely to be the strength of his desire and passion, the strength of the interest he takes in what is proposed. Concentration, memory, reasoning power, inventiveness, excellence of the senses--all are subsidiary to this. No matter how scatter-brained the type of a man's successive fields of consciousness may be, if he really care for a subject, he will return to it incessantly from his incessant wanderings, and first and last do more with it, and get more results from it, than another person whose attention may be more continuous during a given interval, but whose passion for the subject is of a more languid and less permanent sort.There may be rather more exceptions to this line of reasoning than James admits here, but the fact remains that this is a salutary lesson for teachers and students. Genuine interest and passion for a question can sweep away all kinds of roadblocks.