Some things we do have pretty simple, predictable consequences, clearly visible from the overall morality of our surrounding worlds. Killing is usually worse than vandalism, at least depending on who you kill and what you vandalize, instituting or depending on slavery is generally asking for trouble, and overall it’s pretty easy to tell what you can do whenever you want and what’s going to eventually bring the prots down on you. But when it comes to the cost-benefit analysis, stealing throws all the calculations off—there are a lot more variables than we expect in figuring out how it affects our dynamic with the protagonists, and thus how quickly doing it will bring us to the ends of our storylines.
How unlawful, exactly, is it? There’s a lot of separating people from their property that doesn’t carry the same moral weight that “stealing” does—let’s face it, semantics matter. If you’re the local ruler, it’s “taxes”. If you have some way of demonstrating that you stand between the person you’re attempting to relieve of his goods and a worse fate, it’s “protection fees”. If the person you’re relieving of worldly possessions died attacking you, it’s “restitution for the inconvenience”, particularly if he started it. (I do, however, recommend avoiding taking sentimental trinkets if you’re taking this step. Families tend to object with sharp objects and Narrative Causality.) Some prots really aren’t opposed to the idea if you’re not messing with them, and some are goody-two-shoes enough that an air of legitimacy will at least keep them at bay.
What are you taking? The first thing to keep in mind is value, whether material, sentimental, plot-related, or all of the above—the more valuable the object is, the more likely the prots are to hammer down your door for it. Keep an eye on immediate impact, as well. Swiping a couple million from a man who has five houses? Barely slows him down. Stealing a horse from a man in the desert? There’s a good chance that’s going to kill him. The bigger the impact, the more likely it is that Dramatic Necessity is going to give you Plot Karma—yes, there are those of us who can avoid it, but unless you know you’re the universe’s favorite poison brat, I’d suggest not assuming that Narrative Causality will turn a blind eye.
Who you’re stealing from matters, but not as much as you might think, and not necessarily in the ways you’d expect. Don’t fall into the trap of assuming that stealing from the protagonists or from third parties they sympathize with is always a bad idea and stealing from your fellow Hands of Darkness or other not-necessarily-good people will keep the prots away (or at least not bring them in any faster). If you’ve already offended the prots with something else, stealing from them isn’t likely to change much except the speed with which they come after you (and, if you yoinked a powerful enough MacGuffin, that change isn’t necessarily going to be an increase); on the other hand, even if you’re confining your predation to other bad guys, what’s to say that the prots aren’t going to come bashing through your peer’s citadel looking for it the following week, realize it isn’t there, and come after you instead—assuming the other Hand of Darkness doesn’t take you out for your presumption first, or even temporarily team up with them to do it? (Trust me, your peers are very good at ‘extreme prejudice’. And at letting the punishment fit the crime. You’ve been warned.)
Take all you want. Just think about what it’s going to get you into first.