Okay, I watched the video in full, and I have several relatively strong reactions.
First, achieving "flow" is, indeed, an important goal in mastering any sport. But Sam totally misses the mark on how one achieves "flow". One can only achieve "flow" when the technical aspects of the sport have become so second nature that one can "forget" them and simply do it. When Sam says that he just tells his students to watch a good kitesurfer perform, and then says "just do that", I wonder what his liability insurer thinks about his video. If you tell a new kitesurfer to just "do that" without teaching them about the wind window, wind direction, how a four line bar works, how to control the kite, etc., someone is going to get hurt. "Flow" follows (and can only follow) technical expertise.
Second, why is this video titled "The Only Variable that matters after 40...."? What does age have to do with achieving "flow"??? I've taught kiteboarding to a lot of young people who were operating too much "in their heads", i.e., totally overthinking everything. Conversely, I've taught a lot of older kiteboarders who had the ability to relax, be in the moment, and just enjoy the experience. It has nothing to do with age.
Third, and finally, achieving a state of "flow" is important, but to say it's the "only" variable that matters is an overstatement and a terrible over-generalization. The most important variable to improvement in kiteboarding is highly specific for each individual. For some, the most important variable is losing 30 pounds and getting in shape. For others, it's getting over the fear of getting hurt. So, "flow" is a nice goal to have, but it's hardly the only important variable.
Sam, thanks for the video. You've offered some interesting ideas, but kiteboarding (any sport) isn't as simple as just going out and doing it without thinking.