Good self-defence should be based on soft skills and hard skills. Two or 3 'hard skills' or strikes which cover the majority of situations.
I have had very, very brief (in the grand scheme of things) experiences with an excellent self defence instructor, in an hour this person could teach so much more than i learnt with the (also very brief) time i spent as a child learning Karate.
Ok, admittedly I was a child, and that was one instructor, one class. They're not all going to be the same. I have to recall being about 7 and being taught a knife disarming, which was basically, grab their wrist, and twist outwards so it hurts them and they drop it. Almost ANY self defence techique starting with 'grab their wrist' is blatently going to suck. If a 9 stone person is attempting this on a raging, coked up 18 stone thug, they are going to have problems twisting their wrist due to 1) strength differences, 2) as soon as the thugs wrist is grabbed he could punch the victim in the head.
It's funny to remember when I relayed this technique to a cousin, still as a child, and I eagerly got them to hold a remote control like a knife. To my at the time, annoyance, they held in the opposite way to how i'd been shown. With the arm bent and the remote control-knife pointing down horror film style. I then did something to the effect of 'No not like that, like this!' (another sign that if you're having to say that, it's not going to work in the real world). Now I realise it was the technique's and system/instructors fault.
Nor was I told "at this moment in time your body is going to be coarsing with adrenaline, your mouth will go dry, your body will shake, you may feel like you need the toilet, this is your body trying to get rid of as much waste as possible so you can run faster. You will go pale as blood moves to the most needed areas/moves away from skin to stop bleeding if cut (been told both, not sure what's right but the first seems more likely). You will get tunnel vision where you can effectively only see directly in front of you, to help you deal with the threat.
Neither was I told that this is all fine, and a combination of adrenaline and other chemicals in the fight or flight repsonse to help me, not hinder me and make me think I am shitting myself scared.
'soft skills' are extremely important in self defence, and these are sometimes common sense.
For fun, let's take former heavyweight champion Lennox Lewis

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Lennox has just left a mates house on a cold december night at about 11pm, there's no one around. Freezing cold he does his coat up, puts his ipod in his ears and sticks his hands in his pockets, and sets off at a slow, begruding pace eyes at his feet.
His house is about a mile away. A short cut across a dark car park can save him a few minutes. Half way across Lennox bumps into a man standing straight infront of him, just half the size of Lennox. Lennox's heart races, this guy came out of no where?. Pulling an earphone out of his ear, Lennox asks "alright?".
"Yeh, sorry mate, do you have the time?"
"Um sure..."
Lennox looks down at his watch and as soon as he does so, the man whips a hook to the jaw of lennox, coming outside of Lennox's periphreal vision (Yes I know Ive spelt that wrong). Lennox having been suckerpunched, topples to the ground ( for anyone who doesnt buy Lennox being knocked down by a single shot, we can presume several other punches would be thrown, or some sort of weapon like a knife used). Lennox takes a few kicks while on the ground before having his ipod, wallet and phone stolen.
Now, consider this.
Why did lennox cross the deserted, dark car park?
Having his ipod plugged in stopped his sense of hearing stopping him from hearing the attacker, which also makes him a target. His ipod is also valuable, another reason he's a target, for having it on show.
Lennox presented very non-confident body language, slow, slumped, head down, hands in pockets, unaware. The predatory mindset of the attacker picks up on this. His head down also stops him from seeing the attacker.
Lennox also let his attacker come right into his own space, and then complied to look down when asked.
(this is probably unrealistic really, as the attacker would just just suckerpunch Lennox with no speaking, if he had slightly more awareness, the questoin could be used)
Now, if lennox had walked with a brisk confident gait, head up, aware of his surroundings. He becomes much less of a target. But what if that alone doesn't work?
As lennox walks, he notices a man walking towards him, and acknowledges him. As the man gets closer, Lennox asks him "can I help you mate?"
"Yeh, do you have any change?" [ still walking closer ]
"No sorry."
"Go on mate, you must do, it's really important, please"
The two are close now, and as lennox talks, he gesticulates with his hands. Appearing perfectly natural, but by doing this he blocks off his own personal space.
"No mate, honestly. I'm sorry."
"Come on mate, I'm not fucking about here, I need some change!"
The man walks into Lennox's splayed hands and lennox pushes one hand, palm out directly blocking the attacker, and does similarly with the other hand, but hadn drawn back to the shoulder.
"Look, I've told you I don't have any money, now fuck off".
"I don't fucking believe you!"
Moving forward again, the man touches against Lennox's palm.
Lennox asks,
"Why do you want change?"
Immediately after this, the man's brain is somewhat distracted. He is processing what he is being asked, and is thinking of his answer.
During this moment of distraction, Lennox throws his much practiced, devastating right cross to the man's chin, followed by either
1) a flurry of punches, or 2) grabbing the man with one hand while repeating strikes with the other hand.
His attacker on the floor, Lennox then surveys the area for othre attackers, then finding there are none, escapes.
"Be first, be fast and be ferocious".
Almost all of this was 'soft skills'. Avoidance, talking the situation down etc. Only the end bit was an actual strike. Generally it is thought that 2 or 3 techniques drilled to perfection, and drilled under pressure (recreating situations, while inducing adrenaline). Are much better than a plethora of techniques practiced only a few times.
During the rush of adrenaline the mind's thinking is impaired and will stick with what has been put into it, like a computer thats been programmed. Generally fine motor is lost and you are left with gross motor.
The 2 or 3 strikes could be a linear strike (punch or palm strike), a curved/hooked strike (hook or slap but landing with the palm of hand), and a thai knee, or edge of boot kick.
There is sooo much generic crap taught about self defence, it is terrible. It should be illegal, seriously. Because it makes people confident in their abilities when they won't work, and it could them killed. If I'd believed my karate instructor and drilled that now, and then got faced with the knife in a different position (like my cousin) I'd be stuck. Same as when I go to disarm and it doesn't work and I get murdered. This is the same for a lot of the other generic, "attacker does this, you do this fancy twirl and they're secured in your grip while the police come" stuff. While your doing this, theyre going to be fighting back and possiby hitting you. I'm not saying that this technique could never, ever work. I'm sure a big enough, strong enough person who's practiced it enough could, if the situation favours him.
Some of the most important things in self defence are
avoidance,
'the fence' (the hand gestures).
contorlling the situation/talking it down.
Understanding your own bodys reactions to adrenaline.
Oh and yes, if you can run away safely, or get away, do that instead!
This is all basics. I haven't bothered covering power transferance in strikes here, I'm guessing most people know in this subforum know the main technique of it. Jaw/chin is main target for punches for KO, once again (as again im sure people know).
Although the effeminate nature of my username may suggest otherwise, my gender actually falls into the male category.