Read The Goblet Of Fire to my kids earlier this year, and it struck me that the Triwizard Tournament about which the story revolves is really a great example of an author wanting very desperately to have her cake and eat it, too. If Rowling has a strength as an author, it’s her ability to write characters we fall in love with and hate (because they’re all of us and the kids we went to school with) and her ability to pace her stories to keep us reading.

But she never was a gamer, and she doesn’t understand games. This should have been obvious with her creation of Quidditch, a game that exists for no other purpose but to catapult Harry alone to stardom, by placing him in the position on a team to always, 100% of the time, win (or rarely, lose) the game for his House.¹ And there are no other sports (seriously, when have you ever been to a school where there is ONE sport?) and they never play other schools (which is kind of odd, because there are WORLD CUPS in Quidditch, aren’t there?)

This was never more obvious than the Triwizard Tournament. Granted, Rowling has a serious problem, here: just making Harry the Hogwarts champion by random draw would be a coincidence of the first water, and unbelievable. Of course, she could have had Moody/Crouch make certain of that by using some previously-unknown spell to make him the real champion, but it would have been a dead giveaway since it is indeed only logical that junior and senior (6th and 7th year) students will be the most capable of doing ANY task in a high school. Plus, of course, it loses the entire reason that Cedric can be killed and for Harry to be hated throughout the book.

So Rowling comes up with the whole fourth champion trick. Which serves every purpose except making any actual sense. Consider: the solutions that everyone but Dumbledore arrives at are quite sensible: 1) Don’t let Harry Compete, and 2) Give the other schools additional champions.
When these solutions are proposed, there is a lot of handwaving about some sort of “magical contract” that demands Harry compete, so that we do not pay attention to the woman behind the curtain who does not want the plot to go that way, dammit! But never a word is said about how it will be enforced. The Goblet, having chosen the champions, has no further role to play in the tournament.² There was no reason that Dumbledore could not have agreed to the quite reasonable solution of having Harry operate under impossible constraints (e.g. Giving Harry only one minute to accomplish each challenge). Or, since all the events but the final were judged, and the judges were under no constraints to judge fairly, by simply instructing the judges to give Harry zeroes no matter how he performed.  In fact, it’s kind of out of character that Maxime and Karkaroff don’t do that.
But even so, who does this magical contract punish if it’s not carried out? Hogwarts? How? Harry? Apparently not, because Harry drags his feet over the Second Task and goes into it completely unprepared, and the Tournament makes no move to punish him for his procrastination. This of course would have been the easiest way for Harry to avoid the opprobrium of his fellow students: just refuse to succeed.

So what can we learn from this? I suggest a few basic lessons: Firstly, don’t make things you have no interest in (like sport and games) central to your conflict. Secondly, if you create something like a “magical contract” it needs to have an enforcement clause. Real things have real consequences. Finally, handwaving to make people stop asking questions rarely works well.

¹This would have been easy enough to fix, by the way, and still let Harry do his thing. The obvious solution would have been to make the Snitch catchable by every player on the team and then make Harry a Chaser who was just really good at finding Snitches.

²This also would have worked as a partial fix. If the Goblet itself had magically spawned the challenges, this would have actually made sense. It would not have continued the tournament until Harry passed (or failed) his challenge, and additional challengers would have had no challenge to fight.