I think that, for me, it's mostly a matter of not wanting to die. I don't think that I've ever ridden at more than 80% of my ability on the track, simply because my instinct for self preservation is too high. At track days I've followed kids who I could see had zero fear, but also zero skill. Their lap times were comparable to mine because they couldn't pick a line to save their lives. I've led a few around my favourite track and it seemed to help them, in a "can't do, teach" kind of way. I've worked in the pits, for a couple of racers, and can do tire swaps, set up suspension, and do other general drudge work, but that's the limit.