After The Design of Everyday Things you will notice every bad door

Fair warning: this book ruins doors for you. Once you learn why you keep pushing a door that should be pulled, you start seeing it everywhere, along with confusing taps, stove knobs and light switches.

The idea that stuck with me is that when people keep making the same mistake, the design is at fault and not the people. That changes how you look at your own work. If a user can't find a button, it's no use saying they should have looked harder. Some examples feel dated, but the thinking doesn't.