Arguably one of the most layered films ever made, Christopher Nolan's 2010 science fiction about corporate espionage in one's mind is one that still makes for interesting topics of discussion and speculation. This article discusses the film's lead and his mindset throughout the film and needless to say, contains spoilers (considering the tiny unlikelihood that you haven't seen this film).
Ariadne: Didn't Cobb say never to do that?
Arthur: So now you've noticed how much time Cobb spends doing things he says never to do.
The film introduces the audience to the world of Inception much like it does to Ariadne (Ellen Page) during the course of which Arthur (Joseph Gordon Levitt) explicitly states that the purpose of a totem is to mark dream and reality state (responding differently to the Physics in both worlds) as long as the totem is under the usage of only its owner. Despite this, Cobb uses Mal's totem throughout the film. Moreover, the film lays out a structure of rules of its subconscious world that the film states that Cobb also doesn't always abide by. Cobb even recreates memories as dreams. There is enough evidence to show that Cobb is a somewhat irrational, unstable man. The film doesn't give the viewer a complete insight to his mind but fifty years in limbo, being guilty of the idea that drove your wife to death and not having seen your children since can probably change a man.
The film depicts Cobb's drive as returning home to his children going to the extents of working for corporations where failure would prove fatal or worse, being subjected to more time in Limbo. One valid criticism of the film is that Cobb doesn't need to take such drastic measures to see his kids again; before Saito, Cobb's likely had many opportunities to have the laws against him undone (one which the movie shows with Saito) , or simply have their grandfather (Michael Caine) bring his children to him. A relatively petty issue for someone who has open ties to the corrupt to deal with for as long he does. Maybe the lack of practicality boils down to the relatively simple yet most complex; human emotion, Cobb's guilt.
Cobb: I need to get home. That's all I care about right now.
Fully aware of the risks, he allows a team of extractors risk an existence in limbo by stepping into his mind and says that getting to see his children again is all he cares about.
Cobb: Never recreate places from your memory. Always imagine new places.
Ariadne: Well, you gotta draw from stuff you know, right?
Cobb: Only use details, a street lamp or a phone booth, never entire areas.
Ariadne: Why not?
Cobb: Because building a dream from your memory is the easiest way to lose your grasp on what's real and what is a dream.
Ariadne: Is that what happened to you?
He even risks his handle on reality by creating from his memories much like Mal, which isn't something a responsible father would let happen to himself for the sake of his children.
Ariadne: These aren't just dreams. These are memories. And you said never to use memories.
Cobb: I know I did.
Ariadne: You're trying to keep her alive. You can't let her go.
Cobb: You don't understand. These are moments I regret, the memories that I have to change.
.. but he can't. For someone who is actively allowing his mind to lose grasp over reality, why is the difference between reality and dream important? Especially when you're using someone else's totem to differentiate between the two. The film suggests that Cobb doesn't care whether or not he's dreaming. A very contradictory man that, by the third act of the film, almost gets to see his children's faces when Mal calls out their names yet he turns away. Why does it matter to a man who is letting his mind deteriorate whether or not he sees his children in reality or a dream? It's possible that Cobb simply doesn't want to deal with the guilt that won't let him. A father and a lover who inadvertently drove his children's mother and his love to her death.
In the final act of the film, Cobb confronts Mal and tells her the truth for probably the first time because he returns home not fixated on whether the totem topples or not. What makes this job so important out of the ones the movie suggests he's had, is that he's (probably) forced into dealing with his past considering Fischer and Ariadne. He wants to see his children again regardless of the uncertainty of the nature of reality (which he probably never cared for but pretended otherwise) and proves that he's moved on from his guilt. Much like the director himself says about the ambiguous ending:
“The way the end of that film worked, Leonardo DiCaprio’s character, Cobb – he was off with his kids, he was in his own subjective reality,” “He didn’t really care any more, and that makes a statement: perhaps, all levels of reality are valid.”
..that it made a statement about Cobb's emotional state; like the entire film does but, given the grand scale of dream and reality, pretends it doesn't. This article essentially just states in words what this brilliant film portrays in a complex man but doesn't place as much emphasis on for the sake of, hopefully, speculation and discussion.