Cobb: Downwards is the only way forwards.
Cobb: I came here to tell you... something.
Cobb: Something that... you once knew to be true.
Saito: [remembering] Impossible...
Cobb: I can't stay with her anymore because she doesn't exist.
Mal: I'm the only thing you do believe in anymore.
Cobb: I wish. I wish more than anything. But I can't imagine you with all your complexity, all you perfection, all your imperfection. Look at you. You are just a shade of my real wife. You're the best I can do; but I'm sorry, you are just not good enough.
Cobb: If I get on this plane and you don't honor our agreement, when we land, I go to jail for the rest of my life.
Saito: Complete the job en route. I make one phone call from the plane. You'll have no trouble getting through Immigration.
Cobb: I knew Inception was possible because I'd done it to my wife.
Cobb: I'm going to improvise. Listen, there's something you should know about me... about inception. An idea is like a virus, resilient, highly contagious. The smallest seed of an idea can grow. It can grow to define or destroy you.
Cobb: I miss you more than I can bear, but we had our time together. I have to let you go.
Cobb: Inception. Now, before you bother telling me it's impossible...
Eames: No, it's perfectly possible. It's just bloody difficult.
Cobb: I need to get home. That's all I care about right now.
Ariadne: Why can't you go home?
Cobb: Because they think I killed her.
Cobb: Thank you.
Ariadne: For what?
Cobb: For not asking whether I did.
Cobb: I think positive emotion trumps negative emotion every time.