**TL;DR** *The duration of a fight bares no relation to the risk of injury as clearly demonstrated by countless matches. Attacking first leaves one open to very serious legal repercussions. Expecting to be attacked at all times and places is a mark of paranoia.*

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The duration of a fight has nothing to do with your probabilities of being injured.

The nature of the attack does.  If the attacker wants to kill, they will stab/shoot to kill. The aim is to kill the target and leave. If the hit fails, they will try again later. If the attacker's aim is to inflict pain, then they will only stop if either when they have inflicted enough damage (whatever that is) or they are taken out. In both those cases, expect the attacker to plan the ambush in such a way as no matter what the victims does, they cannot escape.

The skill of the attacker does.  If the attacker is a wee mean drunk unable to stand, their attacks are not going to hurt. Just dodge. If the attacker is Chuck Norris... Well, we know how that ends. I heard that a rattle snake bit Chuck Norris and after three days of agony, the snake died. 

The proximity to your mates does.  If all your mates from the martial art club, marines, and special forces are a minute away, the longer the fight lasts the less chances you are to get hurt. You are more likely to get hurt in the first minute than the tenth!

Boxers, MMA, and other contact sport demonstrate this all the time: The longer a match last, the more injury?  Nope. The longer a match last, the more the pair are evenly matched.

You might argue that someone trying to kill you is not comparable with a MMA match. That is fair. However, not all self defence situations involve someone trying to commit murder. A bar brawl is most of the time less violent than an MMA match due to the practitioners lack of coordination and skill.

***Act first, act fast* is utter rubbish.**

It is one of the common tropes that gets totted by deluded people who claim to know anything about self defence. It reads sensibly in the face of it but as soon as you think about it in depth, its sheer stupidity comes to the front.

*I am not lawyer, nor do I play one on TV*.

Acting first makes one the attacker. The situation was escalated form an argument (possibly loud and obnoxious) into a physical confrontation. Any LEO will arrest whoever started threw the first punch. Prosecutors will argue that the attacker is a violent individual and Judges will listen to them. After all, the attacker does a violent sport those aim is hurting people -- a skewed definition of martial arts.

Self defence does not give one unbridled rights to hurt, main, cripple, or kill one's attacker. What the legal definition of self defence is varies from country to country. *If you want to know more, talk to your local lawyer/solicitor.*

Self defence law is complex and depends on your locality. Anyone claiming that their magic formula will save you from legal ramifications is conning you. Whether you are hit first, threatened with a weapon, or assaulted verbally, does not give you a carte blanche to act like a thug. *If you want to know more, talk to your local lawyer/solicitor.*

In addition, people who rely on either violence or the threat of violence to resolve any confrontation are called bullies. It makes one a despicable person most people do not want to associate with.

However, even if it were a good idea legally, the statement would still be utter rubbish form a training point of view: no one walks around expecting hidden and invisible ninja attacking them at any moment. It is impossible. Even soldiers in the middle of battle have trouble detecting attacks. And they are trained for combat. After some time, PTSD starts affecting them -- or combat fatigue, whatever you want to call it. 

Let's assume you want to go down that path.  You have to watch for ambushes, expect the worst of all strangers, and watch out for hidden dangers all around you. This is what the medical profession called [paranoia][1].

Now, in your paranoid state you thought someone is coming close to you, hands in pockets. Is he going to stab you? Yes, quiet possibly. So, react first: pick you gun and preventively shot him in the face! What if you get it wrong? What if that guy just did not see you and bummed into you. He was thinking about his wife and what she wanted for their anniversary, just not paying attention to his surroundings...

Is that how you want to live? Always afraid for your life, never being able to stop and rest. What kind of life is that?...

Of course, you can come up with lots and lots of imaginary situations where this advice saves your live. But they remain *imaginary*. In real life, this advice is utterly useless.


  [1]: http://www.oxforddictionaries.com/definition/english/paranoia