9. CPR Is A Miracle Cure
In a 1996 study by the New England Journal of Medicine, it was found that the movie CPR success rate was as high as 75%.
Usually following someone being dragged from a lake or unexpectedly keeling over, the scene will likely feature a couple of intense minutes of frantic chest pounding and shouting before the person comes spluttering miraculously back to life. If the character is doomed to die, the first-aider will usually abandon CPR after a couple of minutes.
In reality, CPR will very rarely bring somebody back to life. This is not because it is ineffective, but because that's not what it is meant to do.
Chest compressions are supposed to artificially keep blood flowing around the body, not restart the heart - to do that you will almost always need an electric shock. This is why it is vital that you keep administering CPR until help arrives.
In Movieland, if CPR isn't working but dammit-you're-not-gonna-lose-them you can always just start hammering your fist into their chest. Preferably whilst shouting.
This is called a precordial thump and should only be performed once by a highly trained medical professional in front of witnesses when there are no other alternatives - any other time and you're just giving a corpse a beating.