In December 1972, Eugene Cernan took a long climb up a short ladder on the lunar surface and became the last human being to set foot on another world. It was forty years ago this week that Apollo 17 completed its quarter million mile journey home, marking the last time to date humans have traveled more than a few hundred miles from earth.

Imagine if we were to speak to those fabled ancestors who gazed up at the Moon for thousands of generations: what might shock them more—hearing that we actually went, or that once we did we’d barely caught our breath before losing interest? What pair of facts could better illuminate the two faces of human restlessness?