As Good As It Gets (1997)

Revealing mistake: At the beginning of the movie, when Melvin catches Simon's dog, he holds it away from him, with his arms stretched. When the dog begins to pee, you can see that the urine is coming out from Melvin's glove. (00:01:30)

Melvin Udall: I've got a really great compliment for you, and it's true.
Carol Connelly: I'm so afraid you're about to say something awful.
Melvin Udall: Don't be pessimistic, it's not your style. Okay, here I go: Clearly, a mistake. I've got this, what - ailment? My doctor, a shrink that I used to go to all the time, he says that in fifty or sixty percent of the cases, a pill really helps. I *hate* pills, very dangerous thing, pills. Hate. I'm using the word "hate" here, about pills. Hate. My compliment is, that night when you came over and told me that you would never... All right, well, you were there, you know what you said. Well, my compliment to you is, the next morning, I started taking the pills.
Carol Connelly: I don't quite get how that's a compliment for me.
Melvin Udall: You make me want to be a better man.
Carol Connelly: ...That's maybe the best compliment of my life.
Melvin Udall: Well, maybe I overshot a little, because I was aiming at just enough to keep you from walking out.

Trivia: Betty White was originally cast to play Helen Hunt's mother, Beverly Connelly, but she objected and withdrew from the role because the beginning of the movie has Melvin Udall dumping Verdell down the garbage shoot. Betty White is a huge animal rights activist.

Question: Why does Melvin struggle to look Carol in the eye? Is that something to do with his mental illness?