Three years ago when we moved into our house, the stones of our patio were newly laid and all level. Since then we have been walking across that surface, usually along the diagonal between the patio entrance + shed door and the front door of the house, sometimes around the corner to the compost container. Every step we’ve taken has caused a stone to settle infinitesimally into the substratum. Every step the kids have taken has on average made a slightly greater impact as they’ve grown. And when it rains, you can see that it all adds up. If I had a more volatile psychological constitution, this sight would probably be enough to trigger a full-blown mid-life crisis.