I know this is very loose and subjective, but in your many years of experience and observation, just roughly one in how many people who are under some coaching scheme advances to pro level? Pro level can be one who competes in tournaments often and are likely to win, represent their state, or even country. I know that most people train and get frustrated after months of running drills and not being trained the main course and quit. Some expects to see instant results but ended up feeling disappointed and quit because of their unrealistic and overly demanding expectations. It will be frustrating for coaches as well to see that only one in, say 20, 30 or even 100 students stay on for years before turning pro.