So in reading this post over at Robin D. Laws blog over on livejournal, I got to thinking. See, I've been talking a lot about failure here recently. The post on bad rolls making for good RP, and the most recent two posts on the fact that winning should not be a foregone conclusion, and that some situations in a game can even be unwinnable.
However, Robin's post also brings up an interesting counter argument which isn't actually necessarily counter to what I'm saying, as much as it is a qualifier for what I've said. First off is the important lesson that failure isn't, generally, fun. It is in fact losing, and not many people enjoy losing. More to the point, losing "because the GM said so" is really, really not fun. What constitutes 'the GM saying so' is pretty diverse, but I want to point out that in his post Robin is talking about a situation where the GM has put in obstacles that the players are simply not equipped to deal with. So not only is it a loss, but it is an insurmountable obstacle that the GM put there full well knowing (if he/she is doing their job) that the PCs couldn't handle it.
This is important to keep in mind though. In a lot of ways failure takes more work than success on the GMs part. You need to make sure that failure, if and when it happens, does not end the game (unless such is specifically what is on the line for it). You need to make sure that failure is fair when it comes to the player. Most importantly, you have to find some way to make the failure fun. That's right, you have to make losing an enjoyable experience for people. There are ways to do that, most of which I have talked about before and relate to not forcing the characters into a situation but instead letting them choose it for themselves.
Lastly, you need to keep failures balanced. If your players have just had a couple failures in a row, give them some successes. Play up some situations and make them into easy wins to help give them some semblance of being strong back. Losing constantly sucks, so break the monotony. Force the break through if you have to, just make sure to hide the forcing. A couple of big victories can erase all thought of the previous losses, while simultaneously give a real show that the characters have grown.
So keep that in mind when you are considering hitting the players with the real chance of failure. Don't force failure onto them, make sure that what causes the failure is something that they are at least equipped to deal with, and make it a fun experience for them. Even if the characters are dejected at the loss, the Players should still be having fun and enjoying themselves. It is a game after all.