After killing too many people, not helping people or drinking too much Moonshine, a character can become broken.
Broken survivors will not move or scavenge. They will not interact or do any action. If broken for more than one day, they can leave the Shelter or commit suicide.
In order to save the survivors, one other survivor should help him eating, healing. You cannot make to broken survivor go to sleep during the day, as it will not perform any action, so you must wait for the night and put him to sleep in a bed. If it's possible, you should double your guard to minimize the chance of getting raided and avoid his morale situation getting worse.