Steve thank you for this. In writing Ballistic, I came across so much research that makes me think this issue right here is incredibly powerful, maybe the key step in making adults who are more likely to enjoy health and happiness. Ballistic is about a lab in California called P3 that collects granular movement data of elite athletes. They have assessed more than a thousand NBA players, who fit into seven movement categories. One group they call "kinematic movers." They're generally not the fastest, highest jumping, nor tallest generally. But they have great careers because they're neurologically superior at things like landing and cutting, which leads to successful careers and special injury avoidance. This is how we all want to move! This is what P3 trains! And what they find is that when you ask kinematic movers how they grew up, they ALL say they had lots of unsupervised free time in youth. Movement functions like language in the brain, and unsupervised free play is the full immersion learning program. To me it's just like kids who grow up in Quito learn better Spanish then people learning in a classroom in Sacramento. Moving in practice isn't diverse nor constant enough. Kids need to move freely and all the time--seeking fun!--to get the neurological tools to be super fluent. And of course it matters that is essentially the same prescription in Jonathan Haidt's work about preventing anxiety. One definition of anxiety that I love is "the feeling you don't have the right tool for the job." To me, unsupervised free play makes sense as a masterclass in gaining all kinds of tools, including social tools.