Doors open and such for so many reasons it's not even funny. But it's like that saying, "when one door shuts another door open or a window gets cracked."
Something you wanted or an opportunity you were longing for just closed.
Step into your kitchen for a second, first you have a walkway you enter and go through to get to your kitchen, then look around at all the doors you have that are there to be opened. You have the pantry, all the cabinets, fridge, freezer, oven, ect. These are are hypothetical doors. You're literally surrounded but dozens of doors that you didn't even know of.
My point is this, when you think one door is closing or closed itself on you, realize that another door is right in front of you, or besides you.
Don't put your sole focus on the doors that are behind, that's now closed but instead, be grateful that it's closed so now you can move forward and begin to open the other doors at your reach.