> Another purposeful animation is this subtle scale down effect when pressing a button. It’s a small thing, but it helps the interface feel more alive and responsive.

If you haven't watched the Half Life documentary, I can't recommend it enough. In it Gabe Newell talks about the way he wanted the game to be different from games that came before it in that you could interact with things around you so you felt like you were actually in with and interacting with this world. He then related it to a psychological concept (maybe associated with self realization or external validation) and how as humans we crave the kind of physical objective feedback as recognition of our existence and how important and valuable that is. Really a neat idea and whether or not the science is sound, there is something immensely satisfying about interacting with virtual objects and having them respond in a physical manner that replicates physical reality.