He wanted to show that kids like Elmer, the ones that are different from the other kids, are the ones that change the world. The Sissy Duckling, however, was not made into an episode of Happily Ever After, but rather an entirely separate TV special aired on HBO in 1999.
He intended to show that kids like Elmer, who are different from their peers, can impact the world. Conversely, The Sissy Duckling was not included in Happily Ever After; it was aired separately as a TV special on HBO in 1999.