With all the concepts you have learned in the last two chapters, you can build most of the applications you find in the real world. Of course, if you write code with just the knowledge of these two chapters, you should be very tidy because your code will become bigger and bigger and will be difficult to maintain.

Once a Google engineer was asked about how to build large applications. His answer was short and eloquent: Don't. Don't write large applications. Instead, write small applications, small pieces of isolated code that interact with each other, and build a large system with them.

How can we write small, reusable, and isolated pieces of code that extend the functionality of Knockout? The answer is by using custom bindings and components.