In response to "What got left out of software design patterns," Joel Tosi asked what Alexander got wrong in Notes on the Synthesis of Form. To answer, I think it worthwhile to quote Alexander's "Preface to the paperback edition" in full. All emphasis is in the original.

Today, almost ten years after I wrote this book, one idea stands out clearly for me as the most important in the book: the idea of the diagrams.
These diagrams, which in my most recent work, I have been calling patterns, are the key to the process of creating form. In this book I presented the diagrams as the end results of a long process; I put the accent on the process, and gave the diagrams themselves only a few pages of discussion. But once the book was finished, and I began to explore the process which I had described, I found that the diagrams themselves had immense power, and that, in fact, most of the power of what I had written lay in the power of these diagrams.
The idea of a diagram, or pattern, is very simple. It is an abstract pattern of physical relationships which resolves a small system of interacting and conflicting forces, and is independent of all other forces, and of all other possible diagrams. The idea that it is possible to create such abstract relationships one at a time, and to create designs which are whole by fusing these relationships – this amazingly simple idea is, for me, the most important discovery of the book.
I have discovered, since, that these abstract diagrams not only allow you to create a single whole from them, by fusion, but also have other even more important powers. Because the diagrams are independent of one another, you can study them and improve them one at a time, so that their evolution can be gradual and cumulative. More important still, because they are abstract and independent, you can use them to create not just one design, but an infinite variety of designs, all of them free combinations of the same set of patterns.
As you can see, it is the independence of the diagrams which gives them these powers. At the time I wrote this book, I was very much concerned with the formal definition of "independence," and the idea of using a mathematical method to discover systems of forces and diagrams which are independent. But once the book was written, I discovered that it is quite unnecessary to use such a complicated and formal way of getting at the independent diagrams.
If you understand the need to create independent diagrams, which resolve, or solve, systems of interacting human forces, you will find that you can create, and develop, these diagrams piecemeal, one at a time, in the most natural way, out of your experience of buildings and design, simply by thinking about the forces which occur there and the conflicts between these forces.
I have written about this realization and its consequences in other, more recent works. But I feel it is important to say it also here, to make you alive to it before you read the book, since so many readers have focused on the method which leads to the creation of the diagrams, not on the diagrams themselves, and have even made a cult of following this method.
Indeed, since the book was published, a whole academic field has grown up around the idea of "design methods" – and I have been hailed as one of the leading exponents of these so-called design methods. I am very sorry that this has happened, and want to state, publicly, that I reject the whole idea of design methods as a subject of study, since I think it is absurd to separate the study of designing from the practice of design. In fact, people who study design methods without also practicing design are almost always frustrated designers who have no sap in them, who have lost, or never had, the urge to shape things. Such a person will never be able to say anything sensible about "how" to shape things either.
Poincaré once said: "Sociologists discuss sociological methods; physicists discuss physics." I love this statement. Study of method by itself is always barren, and people who have treated this book as if it were a book about "design method" have almost always missed the point of the diagrams, and their great importance, because they have been obsessed with the details of the method I propose for getting at the diagrams.
No one will become a better designer by blindly following this method, or indeed by following any method blindly. On the other hand, if you try to understand the idea that you can create abstract patterns by studying the implication of limited systems of forces, and can create new forms by the free compbination of these patterns – and realize that this will only work if the patterns which you define deal with systems of forces whose internal interaction is very dense, and whose interaction with the other forces in the world is very weak – then, in the process of trying to create such diagrams or patterns for yourself, you will reach the central idea which this book is all about.