There are six very important distinctions that make self-defense different from almost every other subject we teach.
1. Rarity. Emergencies are extremely rare, complex, and varied. Rarity means there is very limited experience available on how to deal with such an event.
Rarity equates with a lack of experience (both globally and personally for the instructor) and an equal lack of reliable information. When there is little experience, people wind up guessing about best solutions.
There is also very little worthy science in this field. A university ethics committee would not approve an experiment on fear and danger. That leaves us with little more than anecdotes. Anecdotes are unreliable. People remember things poorly under adrenaline. Many stories are told to make some group or individual look better. Biases in gathering the information often make the conclusion worthless or misleading.
The modality of the information gathered is also at issue. Videos, while useful, miss the sounds and smells and, most important, touch details. It is very easy to watch a professional MMA or boxing bout and say what you would have done. It is an entirely different thing to act when it is your face being pummeled and you can taste your own blood.
Lastly, there is an industry supplying fantasy disguised as information. One generation of fantasy gets passed on without being tested and in a few years is just accepted wisdom in that subculture—such as the ridiculous assertion in certain systems of self-defense that a particular technique will always get the same result. No one who has fought more than two people could possibly believe that horseshit.
Extensive Experience or Not?
What does this mean to you as a teacher? If you have extensive direct experience, you are a valuable resource. If you don't have extensive direct experience, you can still be valuable as a teacher, but be alert for what you don't know. Be especially alert for things you are sure of, if you can't pick out a basis. You just know a strike to the temple will knock someone out? How do you know? Have you tried it? Did you read it somewhere? Did the people who wrote that article actually try it? How many times? You (all of us) actually know very little reliably. But we tend to "know" a lot of things with great confidence, many of which are not true.
Watch your sources. Be skeptical (including with me).
Don't fret too much. The nature of this beast is that the unknowns vastly outweigh the known. Never forget that as little concrete knowledge as we may have, survival is exactly the problem we evolved to solve.
2) An Open System, Not a Closed One. In a closed system, there are known factors and there are right or wrong answers based on those factors. Engineering is a closed system. A bridge constructed in a certain way, of certain materials, of a certain size, set into a specific type of ground, can safely hold a known weight.
Violence is an open system. The opponent is complex. Size can be a known quantity, but bone and muscle density, heart or toughness, and experience with violence and pain are unknown. Largely, these are unknowns both about the threat (that's the bad guy) and yourself. Will you keep fighting after you feel one of your bones break? Does the unexpected sight of your own blood freeze you? These are things you cannot know until you have experienced them.
These two unknown factors will interact in a complex, moving, and fluid environment. There will be little time; your senses will likely be distorted. The underlying problem is one of incredible complexity.
Many Rights and Wrongs
One of the other hallmarks of an open system is that there are many ways to be right and many ways to be wrong. If a person is assaulted and screams, drawing attention, and the threat flees, that's a win. If a person is assaulted and suddenly shoves the threat hard enough to create space and runs to safety, that's a win. And if the intended victim lashes out and collapses the threat's throat, that's a win.
Conversely, if the scream draws no attention and the threat stabs or shoots the victim to silence him, that's not a win. If the intended victim shoves the threat and runs into a room with no exits, that's not a win. And if the victim collapses the throat of one assailant without seeing the confederate behind her, that's not a win.
And there are results that are only temporary wins. If the intended victim collapses a throat and gets away and either can't justify it to the authorities or can't live with the emotional aftermath, it can be a very dark win. Prison time or turning to alcohol, drugs, or suicide are all losses in the long term.
3) Surprise, Fear, and Speed. No engineer will be asked to build a bridge until after he or she has finished training. No engineer will suddenly be thrown into a bridge-building problem unexpectedly, with unknown resources, working on a bridge of unknown size with unknown material. No building crew will have to work with conditions changing every second. None will have to make every decision and carry out every action under a cascade of stress hormones. No bridge builder worries about being killed if he or she gets a detail wrong.
The natural environment of a self-defense situation is one of surprise and fear in a complex and rapidly changing world. The stakes are high; the margin of error is slim to nonexistent. Whatever the student does must be based on what he can perceive in the moment. The student will have to perform the very first time. There can be no practice runs; there is no way to gradually build up skills through carefully graded problems.
As an instructor, you can never know when a student will need her skills. An engineer can be confident that she will not have to design a nuclear power plant until after she has completed training. Your student may be attacked after the first class, or after a year, or never.
4) The Problem Is Longitudinal. A self-defense situation rarely comes out of nowhere. There are antecedents and aftereffects. Before the problem of physical self-defense comes up—sometimes long before—there are signs and indications. On the other end, win or lose, there are potential physical, legal, and psychological consequences to any act of self-defense. This must be part of your training as well. This factor increases complexity, but also opportunity.
5) The Problem Exists in the Real World. Society does not like violence. And even when it is justified, even when it is absolutely necessary, mechanisms come into play to prevent a repeat performance.
Official legal action might be taken. Injuring someone will be investigated. The long wait for people (who were not there), to decide whether your actions were justified is nerve racking. And even when the police are satisfied your actions were justified, there is always the possibility of a civil suit.
And there are unofficial sanctions. News stories that will question your motivation and integrity. It may come up the next time you are pulled over for a minor traffic ticket.
The people around you will react. Some will tell you to your face that what you did was wrong, even if it wasn't. Others will give words of support but start to find reasons not to spend time with you. You will be punished, sometimes overtly, sometimes not.
Sometimes this punishment will come from within.
There is a powerful taboo against using violence. Even something as minor as setting boundaries is "being rude," and we have all been taught from the time we were babies not to be rude. People want to be surrounded by other people who are predictable and safe and polite. Using force effectively means you are, by definition, unpredictable and unsafe and capable of being extremely impolite.
Defending yourself will always have consequences in the real world. Tough. Defend yourself anyway. It will change your relationship with the people around you, but not as much and in a better way than being victimized.
6) You Are Teaching Students, Not Subject Matter. This is the hallmark difference between self-defense and martial arts.
Every single student is different. They all have different brains and bodies. They will be targeted for different types of crime. The three-hundred-pound linebacker doesn't need to worry about being dragged into a van by a serial rapist, and the 110-pound bikini model rarely needs advice on how to handle a monkey dance, a ritualized fight between young men.
Every student has different resources—mental, physical, and emotional. They all have different limits, lines they will not cross. Some are too arrogant to run, and some could never put a finger in an eye. To teach different people the same things is wasting their time.