My usual response to this question is that my inspiration comes from the world around me. In his book “The Design of Everyday Things,” Don Norman - perhaps THE founder of the usability movement - talks about his experience with doors, and how damn confusing they can be. Is this door a push or a pull? Does it slide? How can I tell how I’m supposed to interact with this very simple piece of technology?
While Norman uses doors to make a point about affordance and signifiers, to me it’s a good illustration of the thought process I have when interacting on the world with a daily basis. I’m always looking at the design of everyday things, especially those that are designed very well or very poorly, and thinking critically about the process that was used to arrive at that decision.