Enter O'Malley. An undead dwarven justicar with an eldritch vortex of infinite pain taking up most of his torso.
He was an NPC that I'll never forget. And he is the result of an encounter that was too high level for the PCs.
This reaches back to the infamous Nick's Campaign (3.5 D&D) that I mentioned in my introduction page. I was a player, and I was a monk, and I hated it. But Nick was such a fantastic DM, and my friends were so swept up in the awesomeness of the sessions, that I couldn't help but get swept up too. Ah, nostalgia.
See, Nick had done something that many, many DMs refuse to do: he posed us, a group of rather inexperienced players, with an encounter that was way, WAY out of our league. He let us prepare for it. He let us think that, with the (then living and quite friendly) Justicar and some townsfolk with pitchforks, we could handle it (what the actual encounter was I no longer remember).
We could not handle it. Not at all. We had to flee. And the worst part, we had to leave the Justicar behind.
To be raised from death.
And to be controlled by a terrible, horrible, evil wizard from Ravenloft named Ian Mcalister.
O'Malley returned a few sessions later, looking bad, but not so bad that we saw his as a threat. He walked right up to our wizard in a tavern an double crit on a surprise attack.
Bye-bye wizard head.
Ian Mcalister had sent O'Malley after us, to hunt us down and kill us with the very man who embodied our failures as a party. O'Malley was our past sins pulling the strings of our future fate.
We fought against O'Malley, his wizard overlord, and countless other abominations in a final-stand fort-defense battle. Our wizard (resurrected, though painfully), used some dark magic tome to cast Finger of Death on Ian Mcalister and save us all.
But O'Malley got away. No longer was he a puppet, but he still harbored a hate for us that could not be satisfied.
And we had sinned again. Our wizard had given in to the dark side to defeat evil, and this set in motion an entirely new course of events.
We were not heroes. We were survivors. We had abandoned people when it put us in too much danger. We had used arcane horrors to fight back the darkness. We had delayed and allowed the forces of evil to muster this far.
But such is war. Lord of the Rings may feature shining heroes without a bit of red in their ledgers, but we've all heard Lord of the Rings. It's over now. Good vs. Evil is no longer an interesting story when the lines are drawn so clearly.
Fantasy books and Fantasy RPGs have gone beyond fairytales and bedtime stories and become literature. They have become about people and their faults.
So give your players something to fail at. Give them situations with no easy answer. Give them hard choices. It shouldn't be a cheap shot, or contrived. It should be organic, and the guilt and regret should come from the players recognizing that their character took on a responsibility, and failed to live up to it.
We tried to save O'Malley's town. But we couldn't. We wanted to. We really did. But we misjudged our enemy. And Nick, the DM, let us do that. He let us walk into a death trap.
Sure, in the long run, fleeing meant losing a battle to win the war. It was for the greater good.
But the greater good should always have consequences in the now. That's why it is the greater good. Because it takes honest roleplaying and hard decisions to achieve it. If it were easy every time, or if the encounter was always winnable, then it wouldn't be a story about the greater good.
It would just be a story about regular ol' good. We have real life for that.