Motivational themes are not just about understanding real people--they can be used to drive stories or messages as well. It is possible to read motivational themes in virtually any kind of prose or poetry, and of course a mismatch between reader motives and text motives explains why some books appeal more to some than others.
I find that certain kinds of literature express a very clear set of values, which can be defined through the motives. Children's literature, for obvious reasons, tends to express clear values even if the plot or characters are highly complex. Motives can be used as a guide to drive characterization and messages: what are the motives that drive the characters? What values do they express? What is the contrast in values between the protagonist and antagonist? What values are expressed overall in the story, in terms of what values are reinforced and which punished by events?
I've been rereading the latter Harry Potter books, and they are fine examples of this, especially as J. K. Rowling continues to elaborate on the characters of Harry and his friends. The values are quite clear, and susceptible to motivational analysis. I'll use this as an example of crafting characters--in reverse, because I feel certain that Rowling's values, while clear, are not expressed in my terms! I'll avoid overt spoilers, and refer to general traits. If I miss something (relying on memory), I'm sure someone can correct me.
Perhaps the biggest theme in HP is the misuse of power and influence; what I would call personalized Power motive. To seek raw power, or petty power over others is a clear marker of bad characters in Rowling's world. For example: Voldemort, of course, commands, and takes on a title of "Lord," which does not exist in the wizarding world, where there are no kings, no royalty, and no nobility, though there is prejudice regarding "bloodlines." But even among the "good guys:" Cornelius Fudge is ambitious of power, and threatened by Dumbledore (GoF, OotP), which indicates immature power motive--the idea that power is a zero-sum game where if you win, I must lose. Similarly, Dolores Umbridge manifests petty power in selfish ways--overcontrol, sadism, and humiliation of those over whom she already has significant power. Even Percy Weasley is described in GoF as being "really ambitious" by Ron, which proves to be true in OoP. His pursuit of petty prestige is evident everywhere--even when doing the right thing, he has to crow about it.
One of the things I admire about Rowling's writing is that she isn't simpleminded about this--the good guys have weaknesses, and the bad guys have strengths. In OoP, Harry makes a serious mistake, partially because he takes over a situation where he really shouldn't have. It is understandable, but wrong. What makes him different from a Voldemort is that he acknowledges his error and matures. He behaves quite differently (but appropriately) in HBP. The difference between impulsive acts and restrained acts is a key indicator of maturity, in the expression of power motive as in everything else.
By contrast with the controllers, Dumbledore is a teacher-- he is happy that his students keep up and hopeful that they will surpass him. He is not selfish, he knows that power divided is power multiplied. He is mirrored by the characters who, for example, admire Harry's ability with a Petronus. He is patient, rarely shows undue emotion, and is always able to appreciate the other person's viewpoint. Note that he always addresses people by their first names, as a covert implication of equality, except on the rare occasions when he feels the need for someone to show appropriate respect where it has been earned (e.g., Harry referring to "Snape," he is corrected at one point to "Professor Snape"). Patience is an indicator of self-control, which allows you to get out of yourself and think of others.
But Ms. Rowling shows other motive themes as well. Positive Affiliation is key: Part of what makes Harry strong is his friends, and when he struggles it is often because he has separated himself (or been separated) from his friends. His great strength, as is stated explicitly in OoP, is his ability to care for others, to love. He even feels sorry for Snape at one point in OoP, against all his years of experience, though he smothers it down because of his own selfish feelings. This is arguably Harry's greatest strength--despite his loveless upbringing, he is still and always capable of appreciating others and caring for them. In HBP, he even expresses some concern for Malfoy, his tormentor of six years! An unusual gift, and I think significant as a driver of the book, since Dumbledore shows the same trait, in spades. One of the few moments where he shows anger is when a student is shaken "violently" in OoP--I think one of maybe two or three occasions in the first six books! (I'm sure someone can correct me.)
Note also that a combination of socialized (mature) Power motive and Affiliation motive is known in the literature (psychological, not fantasy!) as the "missionary profile." This is the motive profile of the reformer and of reform movements in general--caring about people coupled with taking action to have impact: having a positive impact on the world. This is Harry's profile, I think.
Achievement is well represented as well, but it isn't a central driver; it is simply admirable. Hermione's ability to create, learn, and innovate expresses this, as does Fred & George's ingeniousness, though the latter is often addressed to Power motivated purposes--impressing people in some way. Still, their dedicated efforts to perfect things is very much Achievement motivated. Figuring out problems or puzzles, from the first book on, is obviously an important skill, and this reflects Achievement motive.
So we have a clue here to the popularity of the Potter books, in addition to ingenious plotting, vivid characters, a compelling world, and the rest--all three motives are represented! The Achievement-motivated can read it for the puzzles and the endlessly surprising creativity; the Affiliative for the powerful relationships; the Power-motivated for the magic and the war against Voldemort. There's literally something for everyone here.
Hope people found this extremely sketchy literary analysis fun.