Basically every answer I've ever read that involves a "real-world" situation begins with "If you got into a fight, your training already failed you". I know - I gave a couple of those answers.
So, I'm in a fight. What have I failed to do?
I think it really just comes down to one thing. If you made a mistake, the mistake is that you were looking for a fight. It's an understandable tendency among martial artists, especially those that train for the "mean streets," after all; what's the point of training to fight and defend yourself in the mean streets if you don't ever actually use your training?
If we're talking about a fight that happened, only someone who was there can for sure know whether the fight was actually avoidable. Usually, however, we're talking about a hypothetical, and in this hypothetical, martial artists want to "test" their fight theory. If you think about hypothetical situations like that, that could create a tendency to actually go for the fight when there was an option available to avoid it. So constantly reminding ourselves (I really think it's more for personal benefit than for anyone else's) that you always want to avoid the fight will create that tendency when a potential fight situation comes up.
So assuming you weren't looking for a fight, and it happened anyway, any mistakes are of the "hindsight is 20/20" variety. There probably was something you could have done, like not be where the fight happened, even if that meant skipping your friend's birthday party, but then why would you think about the potential of a fight breaking out unless you were looking for a fight?
There's obviously a bunch of common fight avoidance strategies:
But really those are only guidelines that will help you avoid most, but not all fights. What if there's only a sidewalk on one side of the street and there's heavy traffic? What if you just want to enjoy one of the few sunny days outside? What if your job ends late and walking alone is your only option? What if you have to take any job you can get, or else be on the street ('cause that'll definitely increase your chance of getting in a fight)? There's tons of what-ifs, and they're perfectly legitimate as long as you're not looking for a fight. If you were looking for a fight, it's just an excuse to be in a situation where you can test your skills.
If you are someone who's itching for a fight, take up a competitive, full-contact, full-resistance style. Either train MMA, or one or more common MMA feeder styles. You'll get your desire to fight worked out in competition, so when it comes to "real life" you're satisfied. If you're generally conflict-averse, remain conflict-averse and you'll be fine.
Another way you can look at it is like this. If you had no training of any kind, what would you have done to avoid the fight? Did you do it? If yes, there's nothing else you could have done. If no, that was your mistake.
Most likely, you haven't
Now, a lot of "you failed to do X!" discussions seem to assume that perfect situational awareness and response mechanisms are always feasible. That borders on magical/Utopian thinking--in the same class as "true black belts can block any punch!!" Haha--no. Only on television. It's unrealistic to assume that everyone can always be in only safe places, only associate with calm/respectful people, or at all times be observing and managing their situations with perfect aplomb.
But let's assume you've taken "reasonable precautions" about where you are and who you're with, that you have "good" (though not Sherlockian) situational awareness, and yet you still find yourself near to or in a fight. What did you not do? I'd wager:
You didn't back down.
People generally don't like to appear weak or submissive. That's what "losers" are, right? If someone "gets in your face" or claims this is their territory, you "stand your ground," right? Maybe even "take the fight to them." After all, you're a trained martial artist! You have every right to be here. Dammit, you're in The Right! They should back down. Next thing you know, you're in a fight. Getting hit. Or shot.
Because even though you were reasonably careful and aware initially--especially of your external surroundings--you weren't sufficiently aware of your own internal responses. Your anger. Your ego. Your territoriality.
A lot of martial arts schools teach "how to fight." How many teach "how to avoid a fight" or how to calm down a situation"? Not so many. In theory, many teach a little Zen-y mumbo jumbo, or do a little meditation. Not many do much work on that moment of escalation, where everyone's emotions and territoriality are flaring. Not many teach you how to not fight, how to back down, to submit gracefully. That's probably why you're in that fight!
To be a little bit Zen:
You've failed to end the fight.
There could be nothing that you've failed to do. People are like animals, one day you can end up in a fight that you had nothing to do with. To absolutely remove all chances of having a fight you would have to live your life in a vastly different way, eschewing human contact altogether, and you would probably still end up fighting - fighting the wild squirrels/monkeys/whatever to get your food.
That sort of answer is usually proffered by pontificating fools (they do exist, even in MA circles). Theory around de-escalating fights, managing crowds, soothing people's feelings, etc. is add-on humanity type stuff that some instructors teach and isn't strictly included in any martial art. Nor should it have to be - you can go to other classes to learn that stuff. Techniques that work for one person in one situation may fail miserably when used by someone else some other time. The quoted statement makes the very large assumption that you could have or should have walked away. Situational awareness (which is something that is learnt from martial arts) and experience will sometimes say that you should stay and fight (even if momentarily).
Sometimes you cross paths with a douchebag. The reason why martial arts and self-defense classes actually teach you how to hurt people, and not just how to run away, is because some situations are unavoidable.
I have found that the more useless the martial arts school, the bigger the emphasis is on running away rather than fighting. That being said, the best thing to do to avoid a fight is to not go to places where idiots hang out. And don't wear your TapOut shirt. Those things are douchebag magnets.
Maybe you failed to do everything... maybe you failed to do nothing. Its one of those quotes that may make an old master seem wise in a movie, but its basically just a noble sentiment that falls apart on examination.
Sure, perhaps you're out wandering in the wrong section of town... or didnt cross the street when you should have... or you're in the wrong night club. Maybe when confronted your ego compelled you to try to save face. Those sorts of things may indicate that you weren't being proactive in keeping yourself safe.
On the other hand, what about home invasions? predatory criminals? or predatory government in some parts of the world? Violent, mentally ill people? Like it or not, random, no-fault-of-your-own violence occurs. Short of locking yourself into a cold war era bunker (and even that has its limits), you cant be guaranteed of anything. Thats why we train.
And that of course ignores the cases where the violence isn't meant to be avoided. For example, a police officer purposely engaging in it to protect others.
Your training hasn't failed you if you're not training conflict avoidance/resolution in your dojo. Rather, your lack of training has failed you.
You have to specifically train how to read body language, detect warning signals, and recognize potentially dangerous situations. These skills are usually relegated to a weekend seminar, if taught at all. When we hit the mat, we're kicking and punching, not talking and thinking our way out of conflict.
If you're not receiving this kind of training in your dojo, you're going to have to devote time to it out of class. If you'd like to learn more about how to recognize dangerous situations and how best to avoid them, read The Gift of Fear by Gavin DeBecker.
After spending years in Martial Arts , somethings get clearer to you. First of all , I am in MA for 12 years in distinct disciplines like Kick Boxing , Ninjutsu , Wing Tsun and BJJ. I am happy to combine these and Kali/Escrima. For those years , I took many blows during both training and competitions. Still taking. But in real-life , I have never been a tempered man. It is really really hard to drag me to a fight. Because , I accept the fact that , If I start fighting , I can die or I can kill. So if I am going to fight on street , it must be for a reason worth killing and dying. When I get angry to a person , I always imagine we fought and accidentally I killed him or broke his limb. He might loose a leg or arm/hand forever if i break it badly. I concentrate on aftermath. Do I feel guilty ? Was there any other option ? Did my ego cause this? As a Muslim , when i die , i will be questioned for killing this guy. Do i have an ultimate reason? If i had another option and not taken it , how am i going to explain why i didn't?
If you think that way , you will never take that dangerous path to home. You will never fight with a person because he talked you badly or insulted you. I am a strict Kant moralist (Immanuel Kant). Results are not important for me. Intentions are. If there is even a slightest chance that I might kill someone during a fight , that means I took that risk by starting a fight. Taking that risk , means responsibility. The degree of necessity is the distinction between me and a murderer. So if the trouble found me and I have nowhere to escape , I fight with all I got. This is also an important key to win fights. If you fight for weak reasons , you will be weak.
Mostly, your ego puts you into a fight. A guy says something , you don't back off. Because your ego dictates you. Even if you are the right side , saying okay and backing off won't change anything for you or for rest of the world.
And all these ideas tend to shape with your training. More training means more sense of responsibility for a person who is conscious. Of course if you don't have a teacher who trains you like an attack dog rather than a human being.