It is aptly titled, The Big Ball of Mud. And it is, appropriately enough, an essay about the most commonly used design pattern. You might expect that it is about how horrible it is to have a mess. But there is more here than that. Rather it is about how messes arise, what messes do right, what you can do about them, and what you can learn from them. (Which is a lot more than might think.)
If you have never worked in a big ball of mud, and your code would never evolve into one, then there is no point in your reading this. You either lack the experience needed to put the points made into a proper context, or else you are not a mere mortal like myself. But if you are an experienced mortal, you may find it worth the read.
Oops, big ball, not great ball. *blush* (I left the title alone.)