I believe Szu Tzu is right as far waging war goes.
Not everything is about war though.
I'm interested in martial arts in part for self defense and the other part, the "art."
Self-defense, Sport, and Internal peace are the main focus's of martial arts. If we are going for practical self defense, I'm actually very partial to Bruce Lee's philosophical take on martial arts.
Lot of people think Jeet Kun Do is a style, but the heart and core of Bruce Lee's martial philosophy is that that there is 'no style'
The problem with 'styles' is they're full of rules. You have to follow them. But real fights don't follow any rules. That being said, what's the point in following rules of a style?
In Karate there is this concept (I just recently learned of it) called Shu Ha Ri.
-source
Learn the rules, break the rules, recreate the rules. Fill your cup, then empty it.
This goes along a lot with Bruce Lee's philosophy of 'no style' and 'being like water.'
At first glance, it also seems to be the heart of MMA fighting...except the problem with MMA being that its mostly learned for the ring, a place full of 'rules'
MMA was never on Bruce Lee's level.
When it comes to the most pragmatic approach to self defense theory, there is one guy that I really peel my ears open and listen too.
Bae313.
Below is a video he post about why Escrima sucks. (don't worry, he made a following video about why its great)
Guy's an old marine and I thought he was full of crap at first like a lot of people who talk about fighting on youtube, but after listening to him, I had my mind changed. He just made sense.
Not that I would let it stop me from learning Escrima (any self defense knowledge is better than none) and there are merits to learning besides the self defense aspect.