The discussion of villain motives left out one of the basics: power. Or rather, of course, POWER!, possibly with some bwah-hah-hahs attached. Which is often treated as one of the silly, irrational, possibly insane options, but I think that’s missing the point a bit. Especially with some of the people we see getting power in the real world, where their motivations look suspiciously villain-like.
Firstly, power implies security. “If I rule them, they can’t hurt me”. Which doesn’t always work, of course, especially if you give more people motives to hurt you, or you break a lot of laws in pursuit of power - but still, I can fully believe that a basically-sane person with a sense of insecurity (perhaps down to a bad childhood or something, if you insist on in-depth explanations) would pursue power for that reason, and rationalise a lot of fairly horrible things along the way as “the only way I can make myself [and perhaps my family] safe from the cold hard world”.
And secondly, well, there’s the basic monkey-brain thing. The troupe alpha gets first choice of the nice fruit and the mating options. I’m pretty sure that a lot of impulses towards acquiring power (and wealth, which buys that sort of alpha appearance) come from that deep, and get rationalised on the way up towards action. It’s not terribly smart - one can these days get good food and a sex life without obsessively pursuing power - but monkey-brain stuff rarely is.
From the same topic, regarding the idea of a “Detect Evil” power… One place where the last season of Jessica Jones got a little odd (spoilers follow, obviously) was the introduction of a character who appeared to have a “Detect Criminal” ability. (With the twist that it gave him screaming headaches, so you got a rather amoral character who was driven towards virtue because the alternative felt like he was getting an icepick between the eyes, but if he could live with that occasionally he had a great blackmail business going.) Insofar as this was rationalised, the idea seemed to be that he actually detected psychopathic tendencies, which sort of works insofar as they may have a physical basis and are detectable by mundane psychological testing, but having him tell another cast member when she was slipping from hero to anti-hero status because she was making his head hurt then became a slightly iffy plot point.
I think that “power over others” is a common and basic enough human motivation that pursuing it can’t be called insane. Some people with that urge manage it without actually breaking the law, by working in a hierarchical organisation and scrabbling for promotion, or by bossing their own families around; the former can even be mostly harmless, if the person retains a few ethics and a bit of empathy. But on a petty level, it all too often produces annoying managers and domestic tyrants, and on a grand level, it produces politicians who lose the plot and classical Bond villains. And everyone but the Bond villains probably avoids being a villain in their own head by believing they get things done or genuinely know what’s best for the community.
Oddly perhaps, the lust for power isn’t listed as such in things like the Seven Deadly Sins. But then, those lists were generally created by people in a position of power.
The desire for security — for oneself, one’s family, or one’s wider community — is entirely understandable, but can lead to a lot of villainous behaviour. It can be expressed as a pursuit of wealth or power, but it can also take purer forms. It’s the classic motive for a terrorist who started out somewhere reasonable, after all, but it’s also often there in the ruthless amoral businessperson who worked their way up from the gutter. It’s probably too easy for people whose lives are already fairly secure to underestimate how strong it is, but for those impoverished drug dealers still living with their parents, security may be a real dream. Drug dealing is a lousy way to chase that dream, if course, but bad choices happen.
So the classical fascist state is probably led by someone whose motivation is Power, and who offers the population Security if they’ll just flex their morals enough to act like fascist goons. Security may well be the most common motive for the villain’s minions, in fact, and gets around the need for self-justification; the Sopranos-style Mafia goons do know that society labels them as criminals, but it’s a cold hard world, dogs gonna eat dog, so what can you do about it? At least they can care for their families…
“Bad choices happen” is a very important point. It’s a truism in the real world that criminals are dumb. A clever villain who makes one or two dumb mistakes but has completely sane motivations seems emtirely plausible.
Yes, that’s one of Lisa J. Steele’s points in GURPS Mysteries: real-life crime isn’t a good model for an RPG mystery story because so much of real-life crime doesn’t have interesting adversaries, doesn’t have rational motives, and doesn’t have resolution.
A thing I often say is a quote for which I’ve lost the attribution, about tragedy being the struggle of good against good. I like my villains to be people about whom the PCs could say “yeah, if I were in his situation I might be doing that too”.
That may require an unusual degree of empathy from the PCs (or the players), though.* In my experience, gamers aren’t usually people with a strong desire for power over others (they sublimate it into a desire for power over imaginary environments or electronic systems, or status in knowledge-based communities), while the heroes they’re playing aren’t usually supposed to want power for its own sake either (these days; let’s face it, Gilgamesh or Romulus would have had no trouble empathising with Blofeld or Doctor Doom). But power over others may be the standard motivation for non-insane lead villains in a lot of genres.
PCs may understand the desire for security as a motive, but may not be able to understand how far it can lead in someone who starts out feeling deeply insecure. That also ties up to “security for my own in-group” as a motive; heroes can get that, but it’s supposed to take the form of noble patriotism or fierce protectiveness of their family, whereas in villains it can manifest as racism, bigotry, or Mafia-style family loyalty.
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*What’s the GURPS definition of “Oblivious” – oh yes, You understand others’ emotions but not their motivations. This makes you awkward in situations involving social manipulation. You are the classic “nerd”…