I admit it: I’m a sucker for reality TV. My favorite reality shows tend to be those where the contestants have to demonstrate some amount of skill–American Idol, The Next Food Network Star, Project Runway. Most recently, my wife and I have become big fans of the History Channel’s Top Shot.

The show is a shooting competition, where sixteen marksmen from different backgrounds (former marine snipers, ex-police, Olympians, semi-pro competition shooters) have to shoot many different kinds of ranged weapons: rifles, pistols, long bows, cross bows, etc. Sometimes they’re timed, sometimes they’re shooting moving targets, sometimes it’s all about accuracy. The show has been great fun to watch, partially because of the addictive reality drama, but more because, well, it’s fun to watch people shoot stuff.

But this week’s episode has soured the show for me a bit, and it’s got me thinking about writing.

The episode was titled “Wild, Wild West”, and the selected weapon was the Colt Peacemaker–the gun used by Wyatt Earp and Bat Masterson. The team challenge was set up like an amusement park shooting gallery (only with real bullets). It was all very fun and old-westy.

But then came the elimination challenge, and the two people fighting for survival had to compete head-to-head. The gun was the same, but the challenge was new: a large target displayed all 52 playing cards in a deck, and the competitors had to play poker. By shooting a card, they put it in their hand, and the best hand won.

And here’s the problem: neither competitor had ever played poker before. They had no idea what strategies to use, and they fumbled around awkwardly trying to create good hands and block the other guys’ hand. The winning competitor had three-of-a-kind with fives, if that tells you anything about how little they knew about this game.

And here’s the kicker: the guy who won the poker game missed two shots, while the guy who lost never missed. So the result of the episode was that the better shooter had to go because he didn’t know the rules of poker. He thought the competition was testing his skills with a weapon but he now discovered he needed to know a card game, too.

I’ve been thinking about this in relation to writing, and I think it’s a trap that writers can fall into: changing the rules.

The obvious example of this is the Deus Ex Machina, where characters are in a situation where all seems lost and there’s no hope, and then a previously unknown force appears to save the day. Yes, the characters are saved and we have a happy ending, but that ending is ultimately unsatisfying because the author changed the rules.

The other side of this is changing the rules to restrict the characters and limit their abilities. My brother, Dan (a marvelous author), likes to complain about how Superman has been abused by various writers and screenwriters over the years: we all can list Superman’s superpowers, but the writers seem to forget about some of them when it’s convenient for the story. Why does he punch when he can shoot lasers from his eyes? Why can he fly up into space and listen for crimes down below, but still manage to be surprised by hidden traps and bad guys? And, most egregious, after the first Superman movie, where he can make the earth spin backwards to reverse time and bring someone back to life, does he ever allow bad things to happen ever again? He has an automatic do-over, a superpowered Mulligan, and we all know he can do it–so WHY DOESN’T HE DO IT ALL THE TIME?

There’s a maxim about writing endings that they must be surprising, yet inevitable. In other words, readers want the thrill of the twist, but we have to say “Oh, I totally should have seen that coming!” When we change the rules late in the game, there’s no way anything can be inevitable, because it has no foundation. We haven’t laid the groundwork, so it’s all new, and it’s unsatisfying.

So, what do you think? Have there ever been moments, in books or TV or movies, where you feel the writers changed the rules at the last second? Did it ruin it for you, or were you able to still enjoy the ending?