- Antibiotics: In fiction, humans have apparently managed to create a pill that can cure any disease save from the really big ones. like cancer. Real life antibiotics though are much less effective, a certain type is only good for some, but never all, bacteria. Oh yeah, it's also limited to bacteria only - they're completely useless against any other type of microorganism.
- Bulletproof Vests: Likely the most (in)famous one, bulletproof vests are effective at stopping any bullet in fiction though in reality most of them are only good for stopping one or two handgun rounds.
- Chloroform: In fiction, this substance can be used to knock out anyone almost immediately. In reality, they would need to breathe it in for a good minute or two before it kicks in.
- Cool Guns (including all trope sub-types like the Hand Cannon): If a fictional character, be it hero or villain, expect it to be a million times more practical (and reliable) in a gunfight that it would actually be in Real Life. The weapons will inevitably (unless it's a plot point Played for Drama/"realism" or Played for Laughs) have Bottomless Magazines, be totally unable to jam, have very manageable recoils, and can be purchased over the counter even by people who can barely feed themselves or wouldn't pass a firearms exam ever (and some who can Hand Wave part of this, like military or cops, just wouldn't have access to them still because of standardization).
- CPR: In fiction, CPR (or mouth-to-mouth) is portrayed as 100% effective and can revive anyone. In reality though, the success rate for a typical bystander doing it is only 8%, and even with proper equipment chances only increase to 37%.
- Defibrillators: Like above defibrillators are treated as magical devices that can revive anyone, regardless of circumstances. In reality, they are only useful for a heart that is beating irregularly and completely useless for one that has stopped.
- Gun silencers: In fiction, gun silencers can make any gun more or less completely silent. In reality though, suppressors can only reduce the sound a bit. (And honestly, the noise of the gunshot isn't reduced by very much.)
- Hypnosis: In fiction, hypnosis can put someone into a trance almost immediately (even if they're resisting) and can make them do anything the hypnotist wants, including post-hypnotic suggestion. In fact, it takes considerable time to put a subject under even if they're cooperating, doesn't work on everyone and can't make someone do something they don't want to do.
- Infrared Cameras: Walls are very good at stopping heat. So is glass. Infrared cameras thus don't work very well through walls in reality. Fictional infrared cameras though can see through them just fine.
- Katanas: This sword is often portrayed as the ultimate versatile weapon, capable of slicing through anything, including bullets out of thin air. Of course, this is very much not the case in real life; trying to cut a bullet that's flying towards you is next to impossible unless you're lucky or it's a special gun designed to fire slow moving bullets.
- Noise Cancelling Headphones: Fictional headphones can cancel all noise, creating complete silence. In reality they can only cancel continuous emitting sounds such as buzzing or humming and is ineffective at almost any other sound such as people talking, music playing and so on.
- Poisons: Real-life poisons are slow to act and effective only when the victim is given enough of it (which is hard, since most poisons taste horrible and they'll likely spit it out). In fiction, though, one drop is enough to make anyone drop dead immediately.
- Water: Water can be useful at reducing fall damage both in real life and in fiction, but only up to a certain point. Due to water tension you might as well be landing on concrete if you jump into a body of water from many stories above, but in fiction there is no limit to how high you can fall from - the water will still stop you from going ker-splat.
Things Are More Effective in Hollywood
it would likely ruin the story. If "bulletproof" things weren't actually bulletproof and the protagonist got shot, either that's the end of your movie or the next 40 minutes would be spent at the hospital watching them recover. Some of the most notable ones are: