High powered nervous systems = high powered personalities. Didn’t Charlie say a trait he looked for in sprinters was an edgy and high strung persona? Combine that with traveling the world and relative fame and fortune and you have a recipe for disaster.
At first glance sprinters like Powell and Gay don’t seem to fit the profile but they are such introverts their troubles seem to be internal battles. My guess is their type implodes rather than explodes like their flamboyant brethren.