- Gunshot Impact - I love it when I read that a character, wielding a .22 calibre pistol, shot a guy and the impact knocked him backward. Even funnier if the bullet knocked him through a window. Folks, a .22, while perfectly lethal, doesn't pack that much of a punch. In fact, I've read several reports in which people shot with them don't even realize they've been shot until after the fact. Reasearch people. Research.
- Exploding Cars - Unless you're driving a Pinto, cars don't usually explode on impact. ANY sort of impact. They just don't. They're designed not to. Get over it. Sure, explosions are big and exciting, but they don't happen all that often. Include them in your work at your own peril and at the risk of being called a hack. Sure, rig them up with explosives, stash nitroglycerine in the trunk (good luck finding that if you're writing modern fiction, by the way) or hit them with a surface to air missile and they'll explode. But slamming into a wall? Not likely.
- Throwing Knives/Stars - Do you have any idea how difficult is is to stick a perfectly-balanced throwing knife into a stationary target, much less a moving one? Moreover, how next to impossible it is for the random untrained dipstick to throw an unbalanced 10-inch chef's knife and hope that it hits with the pointy end? I've read enough passages where people "buried the knife up to the hilt" in muggers, intruders and monsters that I'm starting to believe that America is populated with nothing but circus performers. Folks, it doesn't work. Throwing stars work basically the same way. The other tines on the star would actually prevent it from penetrating very far. They're more an annoyance and a distraction than they are lethal. Plus, most folks seem to want to aim for the head or the chest, ignoring the fact that the body has a wonderful protective system for such things. It's called bone. Look it up. Fairly tough stuff.
- Knockout - I've been knocked out a few times. I've also taken more than my fair share of hits to the head (no comments, please). I can tell you beyond any uncertainty that knocking a person out isn't as easy as the UFC fighters make it look. Also, getting hit in the head with a board will generally not knock you out, but you will get a nasty concussion, a severe headache, and be disoriented for a while.
- Amnesia/Regaining Memory - Amnesia is the result of a few specific types of trauma to the brain, either physical or psychological. There is no "hit him in the head and it'll all come back" situation. It just doesn't happen.
The point here is simple, and one I've tried to make before: Research. If you've seen it in the movies, that doesn't mean it's true. Most of the time, it means no way on Earth could it happen. If you're thinking of using a clever plot device, do the leg-work and make sure it's possible. In some situations, try it out yourself to see if it works (and no, I'm not advocating blowing up cars, throwing knives at people, or attempting other acts of random stupidity). If you want your work to be believable, show things that can be believed.