AS for all those mistakes I make - they are on purpose - to teach you how to deal with them

If you think of the product as a service, then the separate parts make no sense - the point of a product is to offer great experiences to its owner, which means that it offers a service. And that experience, that service, comprises the totality of its parts: The whole is indeed made up of all of the parts. The real value of a product consists of far more than the product's components.

User experience is really the whole totality. Opening the package good example. It's the total experience that matters. And that starts from when you first hear about a product experience is more based upon memory than reality. If your memory of the product is wonderful, you will excuse all sorts of incidental things.

Behavioral design is all about feeling in control. Includes: usability, understanding, but also the feel.

To me, error analysis is the sweet spot for improvement.

Knowing how people will use something is essential

Isn't one of your first exercises in learning how to communicate to write a description of how to tie your shoelaces? The point being that it's basically impossible to use text to show that