This has led a lot of fans (myself included) to wonder if the entire origin story of Joker as we see in the film was all part of Arthur’s delusions of grandeur. It’s entirely possible. In an interview with Collider, Todd Phillips was asked if we hypothetically take the ending to mean that Arthur made up the whole origin story, then does he have any idea what actually landed Arthur in lock up? Phillips said: However, Todd Phillips did give us a little bit of an insight into his and co-writer Scott Silver’s thought process when penning the script.

And he’s not your standard unreliable narrator, he’s also Joker. So it’s almost like a double unreliable narrator, because he could also be… Some of it could be a goof to him, right? So yeah, early on it was a big part of the screenplay where you’d read it and go, ‘Oh, okay, I’m not really sure what’s happening here.’ In a fun way, I hope. Not in a frustrating way.” This is one of the reasons why Joker is infinitely rewatchable. The Joker character is known to play mind games and mess with your head. He’s narcissistic and he enjoys spinning stories. This idea was implemented in Christopher Nolan’s The Dark Knight too, albeit in a more direct way. There, Heath Ledger’s Joker tells different stories to different people on how he got his scars. By the end of it, we don’t know which one of his stories are true, if any. Joker is now playing in Malaysian cinemas. 

Joker  Todd Phillips Discusses if Arthur Fleck Lied About His Entire Origin Story - 65