If you can’t explain it honestly in the manual, then you are probably making a mistake in the way it is designed and people will never be able to understand how it is ever going to work.

One of the things I found to be the most intellectually demanding in building big systems like Mathematica is this whole thing of starting from nothing and then having to build some kind of language and some kind of structure that a lot of people are going to live inside. Can you set that up in a way that is intuitive for people?

If it was built in the way people traditionally think of building applications programs, people would never be able to use it in practice. It would be this huge mass of disorganized, incoherent features. Without some kind of overarching set of principles, your pieces would never fit together.