The RPG Pundit had an interesting piece yesterday on emulation in RPG--specifically, emulation vs. "scripted" games. In this context, emulation is following the rules and expectations of your game world and circumstances. Scripted, in this case, would be a series of pre-set encounters, with a set of defined paths set out.
I don't want to get into absolutes here or trigger any sort of debate--I think all but the most rules-enslaved GM/DM/CK/Referees would admit that being able to go off script and improvise is one of the essentials of good Game Mastery. I want to talk for a bit about resisting the urge to railroad or exert your will in little ways.
When you're a parent, it's nerve-wracking watching your child tottering trying to balance on new roller skates or a bike. But you know that if you never let go, they'll never learn how. Guidance and a gentle helping hand are fine, but eventually they've got to do it themselves.
I think a lot of GMs (even "adversarial" ones) can develop a paternal attitude towards the characters in and players of a game. We think they've mucked it up too badly; they ignored the obvious signs and stumbled right into an encounter they have no business being in. There's going to be an urge to step in and save them. And that curbs both learning and excitement.
I'm not saying never give your players a light at the end of the tunnel. What I'm saying is: wait. Give them that time to figure out something either purely brilliant or just stupid enough to work. They'll feel better about their accomplishment if they pull it off, and they've perhaps learned something if they don't. If you nerf or fiat every encounter the first or second time things fall by the wayside, you lessen the reward and the sense of accomplishment.
I used to have a pretty bad habit as a GM of interceding in those sorts of instances before I really should have. There's no telling how many amazing character rescues and awesome saves I missed because I was worried about the end result.
So the next time something of that sort comes up, don't worry about the script, sit on your hands, and give them time. Let it go--your players may surprise you.