Its not notoriously difficult, what makes it intangable for most players is that they dont understand as well as they need to what exactly they are betting on and what the counts are representing.
You need to be able to "wing it" when you track shuffles factoring the weight of individual cards, imbalances in the size of card segments, how the game and counting system reacts to cards being removed from and added to the game. And how all that related to the instantanious house edge.
You also need a good understanding and confidence in how averages and expected value will come to life. Many times you will find your self placing a bet knowing that you have a 1:7 chance of being dealt an ace and need to know if thats worth putting money out on, which it totally is.
I think shuffle tracking is to card counting what turbocharging is to tuning carbs. YOu need to have a very good understanding of the underlaying mechanicas and variables or you wont have a quality end product, and it may not even be better than what you started with because it wont work at all.