Make sure you have some training. I've never taken serious training but my former martial arts instructor has. He says that if you get into a knife fight, you will get cut, period, almost regardless of how well trained you are. Also, in order to get close enough to use a knife, you have to get close enough that they can take it away from you and use it on them. If they get it from you, they'll be jacked on adrenaline and likely to really cut you up bad.