Doors enable you to go in.
Doors enable you to go out.
Folklore has it that it is bad luck to leave a house through a different door that you entered through.
The direct alignment of two doors is considered bad feng shui. Instead of the energy flowing through a space it will be able to make a quick exit.
An entrance doorway should be open and welcoming.
An exit should be clearly marked given the choice to leave with an indication of where exactly you are invited to leave.
A closed door in many circumstances represents privacy and should be respected. It can also block your view to the outside world. I say, keep you options open and never completely close your door.
A knock on a door represents an opportunity, a persistent knock many go unanswered, in that case you should try the door bell at least once then simply walk away. : )
When opportunity knocks on your door, answer the call, the window of time my not last forever.
That magic door is out there for everyone and you hold the key.