Funny because I never answer my door when anyone knocks. If you're knocking on my door it's because I don't know you, which means I probably don't want to talk to you. Anyone who knows me knows to call or text before they come by.
So you can't finish doing it whatever you were doing (save a document you're working on, etc) or charge your phone a bit in preparation? Or worse for water, fill a few bottles/pots/whatever in reserve?
When I was at my last house, I didn't have kids, and people would knock on my door every day. It was because my block was full of neighbors who were friendly and nice to one another, and not shut in their houses like hermits.
The way many people in the suburbs live these days, they'd might as well live in windowless metal shipping containers.