When someone knocks at the door or calls me I know it's never good. Usually it's a sales pitch, sometimes it's to deliver bad news. It's never a friend calling to catch up or telling me they're in the neighborhood.
People used to show up or call unannounced, but in my mind the reason they stopped is because everyone is so fucking busy. If I drive all the way to my friend's house as a pleasant surprise they're probably not home or in the middle of doing something they can't put off like taxes or chores. Generally the only way to hang out or talk with people is by coordinating our ever shifting schedules.
I know hundreds of people and we're all too fucking busy to see each other.