You might have heard that skeptical coach's assessment of passing in football.
“Three things can happen when you pass. Two of them are bad.”
Or something like that.
If I might digress for a moment, here's this: http://quoteinvestigator.com/2011/10/04/pass-3-things/
Well, have you ever felt that way about answering a knock on your door when you didn't know who it is?
You certainly want to answer if it is a friend or a neighbor. Or someone who might need help. I don't even mind the occasional chat with a politician.
Of course, it's often some brand of disingenuous selling or outright lying.
I suppose a case could be made for using the peephole as a screening device. But I wouldn't exactly feel like a man in full if the day came when I was reluctant to open my own front door in the middle of the day.
I'd revise that quote to make it read this way: “Ten things can happen when you answer the door. Nine of them are bad.”