It seems to be really hard for athletes who have had multiple concussions to quit while they're ahead. The problem seems to be that many have a few concussions and then feel a lot better once they "recover" after a few weeks or months, so they assume they can just carry on. Where are the doctors who will tell them, "you are now at significant risk if you continue playing, and I highly recommend that you retire while you can still have a highly functional and productive life?"