Importance

So why is this person's take important for you to know about?

The reason is that the core concept - that every observable property will be depended on by somebody with enough consumers - is essential context for understanding why Java is the way that it is.

Many of Java's features are intended to give you ways to minimize the number of observable properties of the software you produce.

Private fields and methods are the easiest examples of this so far. If you make fields or methods private then you can start to expect that consumers of that class do not observe them. Thus, if needed, you will not break anyone by changing them.¹