Freebase Dali

I don't think it's necessary to learn fancy ways to defend yourself simply because you think you can't. Are you constantly being jumped or mugged? If so, then sure, by all means, but I wouldn't default to something impractical. When's the last time you saw a guy successfully round-house kick someone in an actual street fight? (Please don't post a video)
Normally, you won't have time to think of all the shit you "learned" in Karate class. You simply have to be able to end the fight first, and a guy whaling one-twos on your face will make that difficult if you're douching around worrying about how ninja your stance is.
Also, getting your ass kicked is one of the best training methods there are, and should never be looked down upon. Leave the ego out of it. Truly not being afraid of a fight, win or lose, makes you a lot more dangerous. I guarantee you that this is true.

That said, if you end up in a position where you have no choice but to defend yourself in a fist fight, just go with your instinct, as that's what's going to take over anyway. But that instinct is going to remain the same as it currently is, regardless of how many books you read.
Good fighters get that way by fighting.
It really can't be said more simply than that.