The most dangerous thing about a concussion is often the second one. The brain remains vulnerable for some time after the first injury, and a second impact during that window can cause damage out of all proportion to its force. This is difficult to act on, because the athlete usually feels ready to return long before the tissue has recovered, and because the pressure to return comes from every direction at once. Protocols that keep a player out for a fixed period regardless of how well they say they feel exist for this reason: the judgment is deliberately taken out of the hands of the person least able to make it.