One of the main themes in the Harry Potter Series is the struggle between the self and the world. The plot of the novels is built around the conflicts faced by Harry Potter, and, to a lesser degree, his friends Ron and Hermione, in their school. Through the mechanics of the narrative, the Harry Potter series emphasizes that the primary challenge of life is to properly set the limits between the self and the world in which one lives. This theme is drawn in both stark and fine lines.
In the opening chapters of Harry Potter and the Philosopher's Stone, Harry's struggles begin with his placement in the care of the abusive Dursley family, whose every action seems directed towards stopping Harry from asserting himself. When pressed for a justification, and permitted only the lies they tell to themselves, the Dursleys cite Harry's wizard background as the reason for their despicable treatment, but these explanations merely rationalize other motives. Petunia is gnawed with envy, Vernon with the fear of anything he does not understand. The Dursleys do not maltreat Harry because they think he is bad; they do so because they are afraid he is good. His entire childhood passes in a world that is against him, and by making such people the opening antagonists in the series, J.K. Rowling sets forth this theme of the series: The primary struggle in life is the conflict between the self and world outside of the self. Furthermore, by making the Dursleys the opening antagonists in the series, she tells us that the destruction of the individual is the cardinal wrong, the evil to which all others are tributary.
Harry's eleventh birthday arrives, and with it his departure from the Dursley household. Having escaped from a world that was entirely against him, he enters another which is against him in parts. Draco Malfoy taunts him, and gets away with it most of the time. Snape oppresses him, and gets away with it all of the time. Topping it off, he is the target of a campaign driven by a would-be dictator. There may be respite, but ultimately it is Harry versus the World.
In places, Rowling illustrates that there are limits beyond which the self may not rightfully go, specifically, that it may not trespass on others. Those who do not respect this principle are the villians of the books. Draco Malfoy embodies its violation; he has divided the world into Me and Not Me—which he calls Pure-blood and Mudblood—and proclaims his desire for the destruction of the latter. The trend reaches its extreme in Voldemort, whose ambition is to gather all wills under his sway.
Rowling goes to some length to clarify where the line between self and other properly lies. As he is introduced, Gilderoy Lockart has a greatly overblown ego, but is regarded as a harmless buffoon. It is not until he reveals that his gains were by the robbery of others, and brandishes force to protect his ill-gotten gains, that genuine condemnation comes. This clarifies the theme: the self is entitled to assert itself, but not at the expense of others.
Further clarification is provided by the house-elves; their concept of self is diminished to the point that they speak of themselves in the third person. Rowling's portrayal of this attitude is not sympathetic; the mildly assertive Dobby is approved, whereas the submissive Winky is pitied. It is not a trespass to resist a trespass.
The series further attacks the idea that selflessness is necessarily virutous. Three of the major villians in the novel—Quirrell, Pettigrew, and Barty Crouch fils—are the selfless servants of Lord Voldemort.
Rowling also devotes space to illustrating the idea that the line between self and other must be a clear one; in this we have both Ron and Hermione for examples. Ron is the next-to-last of seven children, and dwells in the shadow of five older brothers, some of whom have gone on to great accomplishments; as the Mirror of Erised reveals, his greatest desire is to be successful in his own right. Hermione comes from a non-wizarding background, and is incensed that Draco lumps her in with everyone else from a similar background. Ron resents being thought of as "just another Weasley," and Hermione resents being considered "just another Mudblood." They are individuals, and want everyone to keep that in mind.
The strongest confirmation of the theme comes with the climactic scenes of the novels: Harry's direct encounters with his mortal foe. Although at Hogwarts he gains several friends, buffers between himself and the world, Rowling arranges for their absence during Harry's confrontation with Voldemort. In the greatest of tests, it is truly Harry versus the World. And while the world is often against the individual, the individual is not doomed to defeat. Harry emerges victorious.