Human-centered design requires us to observe human behavior with beginner's eyes, so that we can spot the innate ways people interact with the world around them. We call these intuitive and unconscious reactions Thoughtless Acts, and IDEO designers collect photos of them to inspire their work.
I discovered this tree on a sidewalk in Hong Kong; its roots had popped up in the outline of the concrete tiles simply because it was easier for them to grow that way. Nature grows in the path of least resistance, and as human beings, it takes us a little bit more trial and error to figure out what that might be. That's why the lesson of the tree is so useful: It simply adapted and reacted to the interruptions we built into its environment. It turns out, not all thoughtless acts are committed by humans.