The punchline is Rob Liefeld

So the uncle makes a broadway musical about a robot in a sort of Pygmalion plot, and the kid goes to see it, and loves the whole experience, but it gets savaged by a theater critic, and it closes quickly.

So a whole bunch of other stuff happens in the kid's life featuring several emotional lows and a few emotional highs, and then the uncle comes to stay with them for a while. He's kind of a wreck now, and he got a big uncontrollable dog who he named after the theater critic who savaged the play. And the kid starts working on something day and night, and then he goes to talk to his uncle about his failure, and how he shouldn't give up. And the uncle basically says that he has given up, and that the kid doesn't understand the adult world. So the kid walks away sadly, but gives his uncle a sheet of paper with a drawing on it. And the uncle looks at it, and starts crying and laughing at the same time, and he runs through the house singing a line from his musical "Thank you, thank you, thank you/for this precious, precious gift" and we see on the last page that the drawing was a wonderfully detailed portrait of a human hand.