Component-based design is powerful, especially when we use immutable data and unidirectional data flow. It forces me to stop thinking about how different technologies or tools interact. It gets me thinking about the single most important function of each interface element.

When we start building an application, it's tempting to think of every piece as part of the whole. All interface elements blend into the same big picture, until it becomes so big that separating parts of it out seems impossible.

Imagine you had to build a space ship. What a huge task! You'd need some rocket boosters, a couple of wings, life support, and so on. Now consider how you would approach it if one of the constraints was that each moving part of the space ship would need to be individually tested.

Testing is the great divide between designing systems as a whole and designing systems as large collections of small pieces. Component-based design is fantastic because it makes sure that every part is testable.