People like absolutes. Absolutes are comforting. Absolutes make things sound reliable, and what a lot of people want out of training is to hear that fighting isn't as unreliable as it seems. Always go for the groin, because that will incapacitate anyone. Never go for the groin, it's too predictable/will piss of the bad guy. If you hit this point at this angle, you'll knock anyone out. And so on.
Unfortunately, they're usually mostly bullshit.
There's always exceptions; the one absolute that I'm conscious of teaching is that you should never let yourself be moved to a secondary crime scene. That is an absolute, and I think it's a pretty good one, but I'm sure there's someone out there who can come up with a scenario where that isn't true. I might be able to if I think hard enough, but I suspect it gets pretty convoluted. Once you get past that, I try to stay away from them, mostly because reality, in my experience and observation, isn't that absolute. I've been kicked in the groin (without a cup on) and kept sparring/drilling. I've also been grazed while wearing a cup and dropped like a stone. I've seen little guys shrug off punches that made big guys sit down.
And that's just the physical stuff. Start looking at verbal skills, awareness issues, and other larger questions, and things get vague fast. A successful defuse in one scenario might instigate violence in another. With the same scenario, but different participants. The joke that calmed down the last drunk who threatened you might send this one into a frothing rage.
If that's not comforting...it's not really meant to be. Violence is a big scary picture. If you've seen enough violence to not be scared by it (and I've met very few, if any, people who can make that claim), then violence is still scary for your students, and you should be teaching them how to manage that scary environment, not telling them that it isn't really scary because the good guys always win in the end.