Not answering the door
Unless I am expecting someone, I never open the door. Not even if the person is doing an outdoor service. Or a family member that never called ahead of time. I just feel so uncomfortable. I am an adult. Is anyone like this? If it's abnormal, how do you get over this feeling?
I don't like "drop overs" either - but some people don't mind. In fact, I know people whose front door is open all the time, in and out with people - no knocks.
Don't feel ashamed that you chose to be private about the when and who of your own home. People will get the hint, eventually, that they need to let you know when they are to come over.
You're not alone in feeling this way. I really wish I had something profound to say here, but the point is that your home is kind of your place, and maybe you just want to be left alone.
I've had people knock at my apartment door 2 or 3 times since last Winter. I didn't respond on any of the occasions - just woke up the one morning where the guy went to everyone's doors knocking at them, and telling people to move their cars or they were going to be towed. I am fairly certain the other times it was just my one older neighbor who wanted to ask me for money.
If you have company visit you though, try not to be rude. They came all that way to see you, and if they are friends or loved ones, then it might be worth at least stepping out to see them. A call or text before knocking is something I would prefer, though.