Throughout the Harry Potter series, Harry manages to survive Voldemort's attacks and foil his evil plans time and time again, to the audience's constant surprise. Eventually, Harry defeats Voldemort in Deathly Hallows - Part 2 using only an Expelliarmus spell. People wonder how it is possible that a regular Hogwarts student was able to not only escape but also beat one of the most powerful dark wizards that ever existed, especially since Albus Dumbledore himself wasn't able to accomplish this monumental task.
Source：https://www.cbr.com/harry-potter-defeated-voldemort/
