The Dark Knight was released in 2008 and became known as one of the greatest superhero films in the world.
The film reinvented the idea of Batman as a superhero and was a huge success but Christian Bale, who acted as Batman said he felt his performance was lacking.
The Dark Knight was such a huge success because of the performances by the actors, especially Heath Ledger, who acted as Joker.
Ledger was amazing in every scene and used method acting techniques to make his acting be as close to the idea of Joker as he could.
Bale felt that in comparison to Ledger's amazing performance, his acting as Batman felt lackluster and didn't reach the standard he set for the character.
Bale shared in an interview that the realization that Ledger's performance was better shook his confidence.
Another factor that may have affected Bale is the fact that he failed to win an award for his portrayal of Batman while Ledger won the award of Best supporting actor for Joker.
Bale played Batman in the previous film of the trilogy and in the sequel to The Dark Knight and all three films were extremely successful.
When the role of Batman came up in another film, many wanted Bale to act as the superhero again but he turned down the opportunity and the fat check that came with it.