Yona writes, correctly: "Our appearnce/confidence may change with the characteristics of our opponent assume, but we still have a finite skill level."
This is the distinction that linguists call the "competence/performance distinction." Your linguistic competence is flawless; all the information you need to use your language _perfectly_ is stored in your mental grammar. Your linguistic performance, on the other hand -- the _use_ you make of your competence -- is highly variable, according to the language situation in which you find yourself. You probably won't use your language as well when you're exhausted as when you're rested, even though your competence is the same in both cases.
Then Yona asks: "Is it raising this skill level with knowledge and practice that creates, or strengthens, sai?"
Here we have a bit of a muddle; it occurs because of the difference between linguistic skill and most other skills. Where language is concerned, there is a basic core of information that represents your competence. It's not finite over time, because you fine-tune it now and then to make it reflect the current grammar of your language as used by native speakers -- for example, when you learn a new word and understand its meaning, that word gets added to your linguistic competence. But the changes in your competence will ordinarily be minor ones, and the core of information will remain unchanged.
There's never any need to practice the knowledge that represents your competence with your native language.. It's what is called _internalized_ knowledge, and it doesn't have to be practiced or rehearsed. Unlike your knowledge of karate, which you have to constantly practice if you don't want to lose it, your native language competence can only be destroyed by a disease or traumatic accident that damages your brain. And unlike your knowledge of karate, every native speaker of a language who is not impaired by disease or trauma has roughly the _same_ competence; if that weren't true, we wouldn't be able to communicate with one another.
Strengthening linguistic competence is not primarily a matter of adding new information; rather, it is a matter of increasing your _access_ to information you already have, so that you can use it with conscious awareness. The problem isn't that you don't have all the information you need, but that you don't have access to it because you don't have indexes that let you find what you need when you need it. Establishing those indexes _does_ require practice. Improving performance _does_ require practice.
Suppose I ask you for the rule for making English yes/no questions (like "Did you go to the dojo yesterday?"). I can ask you for that rule with almost 100% certainty that you won't be able to give it to me. Instead, you'll say "To make an English yes/no question, you go... 'Did you go to the dojo yesterday?'" That proves you know how to do it -- and it proves that you know the rule for doing it, because you did it right without hesitation -- but it's not the rule for doing it. Most information about your language is stored in your long term memory that way; you don't have conscious awareness of it, you don't have an index for it, and you can't retrieve it. If I ask you for the rule(s) you use to decide whether something is a joke or not.....or the rule(s) you use for deciding whether to make something plural by adding an "s" sound or a "z" sound to it....or the rule(s) you use for deciding whether a word is or isn't a possible word of English....you can't give me any of those rules. You know them all; they're all in your long term memory; but you don't have access to them.
The grammar of English verbal violence is stored in your long term memory just like any other part of your grammar -- but you don't have conscious awareness of it or convenient access to it. That's why -- as Yona goes on to write -- you may feel that you understand your grammar very well, and still find yourself reacting to verbal attacks with the primitive "fight or flight" response. What you're likely to understand about grammar is a set of alleged facts that you had to memorize to pass tests in school; that set doesn't represent or reflect your competence.
The verbal self-defense techniques that I teach are designed specifically to provide you with indexes for information that you already have in your long term memory about responding effectively to hostile language, so that you can _use_ that information consciously and deliberately and strategically. Physical martial arts techniques, so far as I know, aren't like that; they have to be taught "from scratch" and will be forgotten if they're not practiced.