There’s a great little scene in the movie Parenthood . Steve Martin plays Gil, a neurotic perfectionist father who, despite his best efforts, seems likely to raise some screwed up kids. In the middle of a gripe session with his wife (played by Mary Steenburgen), as he complains about the chaos and complications of his life, his elderly grandmother steps in with a story about the time her husband took her on a roller coaster. “You know, it was just so interesting to me that a ride could make me so frightened, so scared, so sick, so excited, and so thrilled all together! Some didn't like it. They went on the merry-go-round. That just goes around. Nothing. I like the roller coaster. You get more out of it.” This little story, to me, clearly defines two kinds of people: those who can handle the thrill of the roller coaster and those who cannot.