Charlie: Dad, uhm... I've been working on a problem. P vs. NP. It can't be solved.
Alan: I think you knew that when you started.
Charlie: I could work on it forever. Constantly pushing forward, still never reaching an end.
Alan: You know, sometimes you want to think that things don't end. But they do.
Charlie: When Mom was sick, I couldn't stop working on it.
Alan: Yeah, I know. I didn't get it. Uhm... not then. And your brother sure doesn't understand why you spent the last three months of your mother's life working on a math problem. But your... your mother. She understood why. Because she knew how your mind worked.