So one of your players, as players are wont to do, gets an Idea. It makes sense both for the character and for the player, it’s mechanically justified (at least by what the group knows), it seems to solve or at least to help solve the current problem, and there is apparently no good reason not to do it.
There’s just one little problem: it’s not going to work. Not because it’s at a difficulty that should render it impossible, mind. No, the problem is that for various reasons, a success isn’t going to do what they want it to, and in some cases, isn’t going to do anything at all. The person they’re trying to get information from doesn’t actually know anything, the magic they’re using doesn’t actually affect whatever it is they’re trying to use it on. Sometimes it’s pretty benign and you don’t mind them finding out too much–we’ll come back to that–but sometimes you don’t want them to know about the factor that’s going to keep their efforts from being successful. At least… not yet.
But either way, just to complicate matters (meaning that you can’t just shrug the whole thing off as it having been too high a difficulty), they roll like a demon. Nat 20. Zeroes on half the die pool. You know, the kind of thing that begs for an awesome, utterly spectacular resolution. On this thing that just plain cannot work.
Great. Now what?
My favorite strategy is giving them some sort of alternate success, particularly if you can afford to let them know that it was actually impossible and they didn’t just not make it. If they’re trying to befriend (or seduce, or whatever) a certain piece of information out of someone who doesn’t actually know, maybe they don’t get the information, but they do get an ally out of the person. If they’re trying to invent something with the wrong components, they get something else, equally impressive but not what they were going for (and hey, isn’t that where most of our own best inventions came from?)
Sometimes, though, they really shouldn’t have an effect at all: most often, this is because of magic that shouldn’t actually work that way or similarly binary limiters. The thing either works, or it doesn’t, and in this case it shouldn’t. It’s a lot harder to make it do something anyway.
In situations like that, I favor trying to come up with some internal justification for why it might do something anyway, in violation of most common knowledge. Granted, either it’s not the something they want, or it tries to do the something they want and doesn’t quite succeed (and provides them with something that could be reason why it didn’t), but it does at least do something, and even its failure is flashy and dramatic. That way, the failure is in and of itself a result, and it feels like the roll wasn’t wasted. The last thing any of us wants to do is waste a perfectly good impressive roll.
What would you do?