That’s like seven questions in one! I’m gonna take em one at a time between any other questions that come in.

Designing for an operating system changes how you think about design. You can’t optimize for one product, or even your company’s portfolio of products, but have to keep in mind the entire ecosystem that includes everything from one finger games to complex business collaboration tools. In some ways it’s harder because you have to test your decisions and systems more thoroughly, but in other ways it’s liberating because the ‘right’ answer is always what’s right for the users and developers. For example when we introduced a way to have actions attached to notifications in Jelly Bean, we knew we wanted to re-use the concept of an action on other devices (like watches, or even TVs and cars). But we didn’t have a system that was strong enough to express everything a developer might want to do. So we had to compromise on a system that was well designed for the common case, but allowed expressiveness on the part of a designer or developer who wanted to break the boundaries.