When designing digital products we, as UX Designers, deal with screens, pages, and page flows. We rarely get physical. Maybe sometimes we make paper prototypes for e.g. website navigation. But typically our experience doesn’t reach beyond digital.
Imagine areas where physical objects and digital applications merge. Think about a smart home use case, where things are interacting with associated apps. Software that, on a digital screen, lets you control the settings of a smart device. If you want to create a really good app for a smart home use case, you need to know how the physical object works.