Seems to me like it's about a friend who's been in a bad place for long, possibly struggling with an addiction of some sort. He reaches out for a helping hand again and again, demanding that everyone go easy on him. The singer has grown tired of it, stating that his friend is in his peril because of his own doing. He suffers because his friend drags him down with him, but can't really bring himself to not answer the "knock knock knock" on the door.
Seems to me like it's about a friend who's been in a bad place for long, possibly struggling with an addiction of some sort. He reaches out for a helping hand again and again, demanding that everyone go easy on him. The singer has grown tired of it, stating that his friend is in his peril because of his own doing. He suffers because his friend drags him down with him, but can't really bring himself to not answer the "knock knock knock" on the door.