Today's user interfaces do not consist of just a bunch of form elements that are cobbled together onto a screen. Modern users experience designing innovative visual presentations of interactive content challenges technology more than ever.
Sadly, we almost always tend to think in pages when we flesh out concepts for web applications, such as the pages within a printed book. Thinking about a book, this is probably the most efficient way to convey information for this kind of content and medium. You can skim through the pages one by one without any real physical effort, read paragraph by paragraph, and just scan through the chapters that you don't find interesting.
The problem with thinking in pages too much is that this concept, which is borrowed from books, does not really translate well to how things work in the real world. The world is created from components that form a system of components together.
Take our bodies as an example. We mostly consist of independent organs that interact with each other using electrical and chemical signals. Organs themselves consist of proteins that, on their own work, like machines to form a system. Down to the molecules, atoms, protons, and quarks, we can't really tell where one starts and where it ends. What we can tell for sure is that it's all about systems of components with inter-dependencies, and it is not about pages.
Modern user interfaces are very much like the real world consisting of systems of components. If, where, and how they are distributed to pages is subordinate while designing them. Also, they should work independently, and they should interact with each other on an interdependent level.
