Diabolus Ex Machina

What makes this trope so bad? Is it because of how the outcome usually goes From Bad to Worse out of nowhere?

More because it's a cheat, I think. Just as Deus ex Machina is a cheesy way to miraculously Ass Pull the protagonist's bacon out of the fire, so is Diabolus ex Machina a dastardly way to kill their hopes.

As an example, consider the notorious Kobayashi Maru test from Star Trek. It starts out as a simple training simulation, apparently testing the subject's ability to command a starship. Then a crisis hits, and no matter what the subject does, no matter how brilliantly he performs, there is no way to save the ship. (Unless he knows about the nature of the test beforehand, and arranges to cheat the computer right back.)

edited 16th Nov '15 5:56:03 PM by pwiegle

The way I see it, a Deus ex Machina is a way for heroes who haven't earned their victory to suddenly win anyway, just because. It's cheap, it's annoying, and it exposes the creator for not knowing how to let his/her characters get out of a jam (or make it to the ending) with things like skill or heart.

The Diabolus ex Machina swings in the opposite way. Heroes who have earned their victory suddenly lose anyway, just because. The problem with it is that it can potentially undermine everything they've worked for or gained, all so there can be a little extra drama or (cheap) tension in a story that probably doesn't need it. There's making a character face challenges, and then there's jerking them around just to make them suffer.