I don’t know whether this will further illuminate my previous point or confuse it utterly, but maybe a little bit about the historical/theoretical underpinnings of the Enmity Clause will help:
The Circles mechanics were born from the Resources mechanics. Basically, my group was playtesting Resources way back when (2004?); we were working on Burning Wheel Revised. I think we were in the midst of the Burning Corso campaign. Anyway, while playing with the Resources mechanics (I think I was buying armor for my wizard after the second or third incidence of a crossbow bolt to the chest from an assassin), I got what I wanted but taxed my Resources pretty severely. I may even have tapped myself out. I suggested to Luke that the system could probably be used to generate NPCs on the fly, just like Resources could be used to generate objects. Luke had been contemplating a system for such a thing for a while anyway, so it was a good spark.
The Enmity Clause (and the Gift of Kindness) occupy the same headspace as Compromise in the Duel of Wits. What had struck me when I was purchasing that armor was that the story changed–it moved forward–but there were also consequences that would haunt me. I say it all the time when asked: the core of Burning Wheel (and Burning Empires) is choices and consequences. My failure had been AWESOME.
When I was talking to Luke about my idea, I tried to verbalize why that was so cool, but didn’t have much success. But Luke understood it better than I did, and the Enmity Clause was born.
So anyway: Enmity Clause and the Gift of Kindness are forms of Compromise. They aren’t as expansive as Compromise, but they don’t really have to be. You have three potential options when you go into a Circles (or Resources) test: Yes (i.e., you succeed and get what you want), No (i.e., you don’t get what you want, you better find a different path), or Yes, but…(you get what you want, but there are consequences that are going to cause you trouble).
In Resources, those consequences take the form of Tax. In Circles, you get Enmity.
So here’s the basic principle: A successful Circles test is like a Duel of Wits that you win without losing a single point from your Body of Argument. You get what you want without compromise. A failed Circles test in which the GM does not offer the Enimity Clause is like a Duel of Wits that you lost without taking a single point from your opponent’s Body of Argument. You’ve used a portion of your Building Scene and accomplished nothing (although you hopefully at least earned a test for advancement in Circles). Finally, a failed Circles test in which the GM does offer the Enmity Clause is similar to a Duel of Wits that you won but you owe major concessions. You got what you asked for, but the price or conditions make you wonder whether it was worth it.
As long as you keep that final bit in mind when offering up an Enmity Clause, your players should stay riveted. Yes, they should feel like they’ve just suffered a setback (sometimes quite a severe one), but it should also cause their brains to start grinding away at a way to turn the new situation to their advantage.
The same holds true when giving yourself the enmity clause as a GM. For instance, sure, connecting your Figure of Note to a sleeper that is under surveillance can hurt you badly. But now we all know, as players, that someone out there is running an intelligence operation. As the GM, you now have the opportunity to position your FoN in such a way as to discover that operation. Hull the guy in charge of it and you’ve just won a powerful advantage. Of course, the players are going to be trying to get to him first…