How many people utilize the teaching in their everyday life? Following the path of least resistance is a key point of the book, yet few people do that.
On of the other main cornerstones is that you do not engage in battle unless you already know you have won. I can assure you almost nobody follows that one.
I'd say following the path of least resistance is endemic in our society. Not for cerebral reasons; more like laziness.
Let's look at your second point: "do not engage in battle unless you already know you have won". Again, I think we're attributing a higher level of genius to Sun Tzu than he deserves. Sure, anyone who's played Civ IV knows that quote.
But, what does it mean? Is it possible to "Know" that you're going to win a battle? No, not unless you have a crystal ball or Miss Cleo as your adviser. So, you can never know 100% that you're going to win a battle. So, if you don't engage in battle unless you "know" you've already won and it's impossible to know beforehand; you won't ever engage in battle! No wonder nobody "follows" that one...
Ok, maybe he meant you don't fight unless you think you can win (i.e. more/better troops, more supplies, advantageous terrain, etc)...well, DUH! That comes right back to the "common sense" argument. Of course you don't fight a war unless you think you can win! Sure, you can fight battles that you think you can't win, but those strategic "losses" would somehow advance your overall strategy. But, again, this seems obvious; fight if you can win and retreat if you can't. I'm no military strategist, but isn't that a basic human instinct?
Maybe he means that you should think positively and always consider yourself victorious even before you fight. Okay, I'll buy into the "power of positive thinking" to an extent, but that's still not "groundbreaking". That's like a self-help book for generals. Heck, Tony Robbins and Dr. Phil should be able to take over the world then, right? Pfffft, no amount of positive thinking can overcome significant military disadvantages.
Where's the military genius in that? I think it's like the Emperor's New Clothes. People like to "feel intellectual" by citing Sun Tzu and ascribing some sort of Gnostic wisdom where there isn't much. Maybe he was a genius for his day, but today, he seems like Captain Obvious to me.
Like I said, I'm no military expert, so if there's any West Point/Annapolis/Etc. grads that want to shed some light on Sun Tzu's genius, I'm all ears.