I recently got my mother to try out Portal. She liked the concept and was okay at the puzzles, but the biggest issue was figuring out how to walk through doors. She could handle the spatial reasoning, but she didn't have an intuitive understanding of how wide her character was. This got me thinking about when I first figured out movement. I think it was in Quake, before there were mouse controls, and the pitch had to be adjusted with the keyboard. I also remember being really bad at it, and alternating between moving around and aiming. It took a while for aiming while moving to make any sense at all. Any similar stories out there?