Throwing a knife like a dart in real life would most likely have it tumble in mid air and be useless. You could make it more aerodynamic, add fins and such, but then what you have is a dart. And as I said before, even a trained throwing knife expert can not simply walk into a room and successfully hit a target on the first go with any degree of reliability.

But, this isn't real life, so we can get away with a little bit of Hollywood physics.

[[I'd put a witty GIF here pertaining to Hollywood physics, but I'm not sure where to find one, so you'll just have to use your imaginations]]
[img=http://stream1.gifsoup.com/view5/2084577/spongebob-imagination-o.gif]