Val passed this article along. The article itself is well worth the read, but the short and sweet version is this: most people cannot actually recognize what a drowning person looks like. They know how drowning looks in the movies, and assume that it looks the same in real life. The reality is, drowning in real-life looks nothing like it does in the movies. In fact, it's almost completely opposite.
Violence is the same way; violence in real life looks nothing like it does in the movies. Especially martial arts movies, which, while they may have very entertaining fight scenes, show nothing that looks remotely like a real violent assault. Some non-martial arts movies get it closer, but even they don't get things perfect.
Unfortunately, many people in the martial arts community have more exposure to martial arts movies than they do to real violence. As a result, they equate one with other, and think that if what they are doing looks like the stuff in the movies, they must be doing "real" fighting.
Obviously, not everyone gets involved in martial arts or combat sport to learn how to deal with violence, but for those who do, it's important to know and recognize the differences. If you can't, go find people who can, and learn the difference. There's plenty of good material out there.