Unbreakable’s Ending Explained (Spoilers)
After embracing the idea that he might be a hero, and stopping a serial killer from murdering two children, after they already killed the kids’ parents, David accepts he is a hero. He even tells Joseph who has been a bit too boisterous about the idea. But, in admitting to Elijah was right all along, Elijah reveals to David is a villain. More so, Elijah is a terrorist who has used simple conversations he has had, alongside all the time he has had on his hands, to cause 100s of people to die.
That includes people on the train that David survived. Thus invigorating Elijah for he sees David as his arch enemy. In many ways, Elijah looks at him the same way Joker does Batman in The Dark Knight. David is to be the person who he duels with until the end of days, but then David calls the cops. With that happening, Elijah, who now goes by his childhood nickname, Mr. Glass, is sent to a mental institution. Said mental institution is where Mr. Glass remained until the upcoming events which will be seen in the movie Glass.