It's impolite not to open the door for someone.
Barry was walking into the hotel and Sally was walking in after him.
Barry wants to open the door.
Barry opens the door for himself and holds it open for Sally to go through.
Barry opens the door for himself and lets it close behind him.
Sally is grateful that she doesn't have to open the door herself.
The door swings shut and hits Sally in the face and breaks her nose.