In classical Greek theater, when a problem was intractable but a solution was nonetheless needed, playwrights would fall back upon a trusty device: They would have a god swoop in and set everything right. This technique is known as deus ex machina--literally, "god from the machine"--so called because the actor playing the god du jour (Apollo, Zeus, whoever) would be lowered onto the stage by means of a mechanical device.
Presumably satisfactory to an audience of Athenians accustomed to such divine manifestations in their daily lives (what were those guys smoking?), this dramatic technique has fallen into disfavor. It's at best the stuff of fairy tales: The rich uncle no one's ever met before suddenly dies, leaving our heroes millions of dollars and allowing them to stave off foreclosure; a lightning bolt strikes down the killer, just as he's about to finish off the damsel in distress. In its most amusing form, it's an "Infinite Improbability Drive" from The Hitchhiker's Guide to the Galaxy, saving Arthur Dent from imminent death as he's shot out of one spacecraft only to be miraculously picked up by another. But more often. as Annie Wilkes, the psychotic fan in "Misery" might put it, it's cheating. And then she'd smash your foot with a sledgehammer. And who wants that?
But what would Annie Wilkes think of the modern antithesis of the deus ex machina? This would be the device where the gods, rather than helping our protagonists, are more mischievously inclined. In these days of relative technological superiority (compared to the ancient Greeks, anyway), our dramatists often need to contort themselves in order NOT to have the heroes escape too easily.
How many times have you seen a "Star Trek" episode wherein the transporters are non-functional due to an "ion storm"? Now, heaven knows ion storms are a pain in the collective posterior: If the Solipsist had a nickel for every time he's been late to work because of an ion storm. . . . Still, it seems to happen all too conveniently for dramatic purposes.
Closer to home, and perhaps more reasonably, think about how many times Mulder and/or Scully (and/or just about anyone in a slasher movie) is unable to get a cell phone signal. Now, this is certainly something that does happen in the real world, but is there something about the proximity of serial killers or unexplained phenomena that plays havoc with cell phones? Does nobody in Hollywood subscribe to Verizon?
The worst example of this sort of thing ("deus ex mocking-us"?) is when someone is fleeing some horror and inexplicably trips. This is especially delicious if the character happens to be some sort of gymnast or otherwise athletically inclined person. The presence of danger not only knocks out cellphones but apparently messes with people's equilibrium as well.
So is it not just as much of a cheat to have conveniently scheduled pitfalls crop up as it is to have a god out of the machine to save us? If writers need gods to spice up their plotlines, for good or for ill, well, God help them then. And God help their readers!