How the Grinch Stole Christmas

I saw this play Sunday night with friends. It's a posthumous stage adaption of Geisel's book. It must be strange for a writer to create a new piece from someone else's work, especially when the original artist isn't around to ask questions. "Ted, what were you thinking when you chose the name Cindy Lou?"

Anyhow...the play follows the book's storyline. The Grinch doesn't like Christmas, so after the "townies," the Whos, shop and decorate for Christmas, the Grinch steals it all. When one of the children befriends the Grinch, he changes his mind about the holiday. Which is all fine and good. But I kept wondering why the Grinch hated Christmas in the first place. What was the source of his anger? How did he get to such a misanthropic place? I don't want to put "the character on the couch" (to borrow a workshopping line from a past instructor), but doesn't this matter? Back story? Context? It could even be a separate story, a character study. I'll suggest it the next time I hear a writer complain of being blocked.