Books and films are formative influences for the people who interact with them; people carry with them the stories they love. This is true for fantasy movies as much as it is for documentaries—books like Harry Potter have a tendency to leave their mark on the people who enjoy them.
In the first book, Harry, Hermione, and Ron find themselves chasing after Voldemort. After Ron is injured, Harry and Hermione continue—only to be met with a test that will allow only one person to continue. Hermione volunteers to stay behind, in order to care for Ron. When she tells Harry that he is a great wizard, he says he is not as good at using magic as she is. She responds by saying while she is adept at books and being clever, that there are more important things that can help in a battle, such as friendship and bravery—Harry may not be the best magic-user, but technical skill is only one part of what will get Harry through this battle. Sometimes, the friendships someone has with others, and the knowledge that their friends will support them, is as valuable as weapons or skills. In the end, Voldemort’s army was no match for the family and friends Harry had; the support they gave him, the courage that support led him to claim, and their own bravery, was enough to triumph.
Later on, faced with an establishment that sought only to control them—and the reality of Voldemort returning to power—Harry and his fellow students banded together during his fifth year to create Dumbledore’s Army. With encouragement from Hermione, and additional help from Professor Lupin and Sirius Black, Harry taught his friends and fellow students how to defend themselves. Dumbledore’s Army was an inter-house effort of students, inspired to fight by a rising willful ignorance about the true situation of Voldemort’s return to power. This group of children—many of them underage—taught themselves and each other how to perform magic that most would have believed beyond their skill level. Instead of accepting this complacency in the face of true danger, Dumbledore’s Army risked almost everything to be involved in the secret society, including torture from Delores Umbridge, whose job it was to keep the students of Hogwarts controlled, so that they could not rise up against the Ministry of Magic, the Wizarding government. (Dumbledore’s Army took up the name of their Headmaster as a kind of sardonic joke at the ministry’s expense—the fear was that Professor Dumbledore could and would create an army from his students to take on the ministry.)
In their seventh year, Harry, Hermione, and Ron left school to find and destroy Voldemort’s Horcruxes in order to weaken him enough to finally destroy him. Snape became headmaster, and known Death Eaters not only openly held teaching positions but also used those places of power to torture students. The remnants of Dumbledore’s Army formed a kind of resistance. When the Death Eater Professors wanted them to torture younger students, they refused, and instead took the punishments themselves. The solidarity and resistance that Neville and the rest of Harry’s friends created lasted long enough for Harry to find most of the Horcruxes—and when Harry returned and needed help to find and destroy the rest of the Horcruxes, his friends did not hesitate to fight and risk their lives to help him or to help defend their school. They were invaluable in the battle that saw the end of Voldemort.
As children and people grow, they take with them the lessons they have been taught from their favorite stories, whether they learned them from a book or a film. The Harry Potter books and movies made sure to teach some incredible life lessons.