Instead of simply providing an answer, I'll provide scenarios from each and then talk about the common thread through the scenarios.
First up is Harry Potter.
In J.K. Rowling's first book, Harry Potter and the Sorcerer's Stone, Harry goes through his first year at Hogwarts, a school for wizards. On his first night at Hogwarts, all the first-year students have to go through a ceremony, in which the Sorting Hat is placed on each student's head; the Sorting Hat reads the student's character and then tells the student which of the four houses within the school he or she will belong to. When the Sorting Hat is placed on Harry's head, it sees inherent qualities in Harry that would allow him to do well in Slitherin, the house that every bad wizard in the history of Hogwarts have belonged to ('bad' in the sense of 'evil'). Harry begs the hat to put him anywhere but Slitherin, and so he ends up in Gryffindor, a house whose wizards are known for courage. In short, Harry chooses to not be a part of Slitherin.
Later on in the series, Harry worries about the fact that the Sorting Hat originally wanted to place him in Slitherin because he thought that meant he was a Slitherin simply posing as a Gryffindor. His mentor (so to speak), Dumbledore, tells Harry that what he has on the inside doesn't define him; rather he is the sum of his choices. And he chose Gryffindor.
Keep that in mind as I move on to the second part of the riddle: the TV show House.
And, finally, comes the third part of the riddle:
In the preface to Mother Night, Kurt Vonnegut writes that this is his only book for which he can provide a moral. The moral, he writes, is this:
We are who we pretend to be, so we must be careful about what we pretend to be.
Are you seeing the theme now? The main character of Mother Night, Howard W. Campbell, Jr., is an American living in Berlin when World War II begins. As a famous playwright in Germany (he writes his plays in German) who is married to a beautiful German actress, Campbell chooses to stay in Germany even as the war breaks out. He becomes a spy for the Americans by sending out messages through radio broadcasts with secret signals in them (the signals are so secret that Campbell himself has no clue what information he is passing on); his radio broadcasts are pro-Nazi. The world sees him as a Nazi because he is "pretending" to be a Nazi. He questions his own motives for what he did during the war:
Those orders I carried out in Germany were ... ignorant and insane .... I knew it. God help me, I carried out their instructions anyway.
Campbell lived his life hiding who he really thought he was; in the end, his true self was so hidden that even he wasn't sure who he was. In my own words, the moral of Mother Night is this: If we don't actively choose who we are, someone else will choose for us; then, when they're finished with us, nothing will be left of us.
Putting all that information together leaves us with an answer to my original riddle: Harry Potter, House, and Mother Night explore the notion that our choices are what make us us, regardless of what we start with.
I can't quite end the post here even though I've answered the riddle I posed because there are other quotes I want to share from Mother Night that struck me:
We are never as modern, as far ahead of the past as we like to think we are.
History often goes hand-in-hand with sports.
All people are insane ... God help anybody who looks for reasons.
"Headache?" he asked me.
"Yes," I said.
"Take a aspirin," he said.
"Thank you for the advice," I said.
"Most things in this world don't work--" he said, "but aspirin do."
"This day will go down in history," said Jones.
"Every day goes down in history," said the boss.
I had previously said that Vonnegut's books make me think, and Mother Night was no exception. The above quotes are just some of what I underlined (metaphorically, as the underlining was done on a Kindle). It's a book that still has me questioning my own ideals and motivations, more than a week after I finished it.
As a final note, I watched the movie Mother Night yesterday (a side note worth mentioning because of my post from last week). While I prefer the book to the movie, the movie did a nice job of providing a visual representation of a complex book. It is the only movie I know that could have "White Christmas" playing in the background as a prisoner is marched to his jail cell in the opening scenes. Another artistic highlight is when Campbell (played by Nick Nolte) is watching a recording of himself that had been taken fifteen years earlier--during the war--speak about pro-Nazi sentiments. You see Campbell's horrified face covered by the projection of his righteously angry face. If that sentence didn't make sense, all I can say is you might just have to see the movie to understand.
Happy reading ... and choosing who you are.