It doesn't seem like knowing your enemy and knowing yourself should actually make you invincible in war. Besides, what if your enemy also knows themselves and knows you?
It makes more sense if you consider that another option is to avoid the war. So I would interpret it like this:
If you know that you are strong and that the enemy is weak, you will win the war. (And if you know otherwise, you will avoid the war -- by keeping peace, paying tribute, or surrendering.)
If you know that you are strong, but you don't know your enemy... sometimes you will win, sometimes you will be surprised by finding that your enemy is strong, too.
If you have no idea, and just attack randomly... expect to get destroyed soon.
In this light, the next quote would be interpreted like: before you start the war, make sure to build a strong army, so that you don't have to improvise desperately after the war has started.
At a sufficient level of abstraction, the fundamental principles of strategy are approximately substrate-independent, I think. They are formless. Void.
what if your enemy also knows themselves and knows you?
IDK what Sun Tzu would say to this, but I would say,
Here is my favorite Sun Tsu quote:
I'm not sure how this actually makes sense in the context of war. It doesn't seem like knowing your enemy and knowing yourself should actually make you invincible in war. Besides, what if your enemy also knows themselves and knows you?
But it makes perfect sense in the context of a debate. Replace "know yourself" with "know the argument for your side". Then replace "know the enemy" with "know the arguments for the other side". Assuming you know both sides and defend the side you honestly believe in, it does seem like you should be invincible in debate. All you have to do is communicate the arguments, and people should agree with you. (It's more complicated than that, but at least it makes more sense than the version about war.)
That leads into this next quote:
In a debate, you should not try to win by getting better at debating. It's more effective to win by first knowing both sides, and then picking the winning side.
How do you know you know both sides? With an Ideological Turing Test, of course: