It isn’t hard. It feels hard! When you walk through a door right before someone else, you need to hold that door open for them, or else you’re rude. But if they’re a little too far behind you, they have to hurry to catch up, and then (as Redditor Voldetitty recently pointed out) you’re actually being annoying. At some nebulous distance there is a phase change from “don’t hold the door open” to “hold the door open”, and misjudging it will ruin your life for as much as five seconds.

In action movies, the hero never has a problem smashing through doors - one solid kick is all it takes. In reality, gaining access to a locked room is much harder; but not always impossible. This infographic "breaks down" how it's done.

Smart doorbells can snap a photo of whoever rings the bell, making it so you can screen all those visitors you get throughout the day. Over on Instructables, Naran shows you how to build one with a Raspberry Pi.

You're a functioning adult with a reasonable intelligence. So why do you keep getting tripped up on a basic thing like opening a door? It's not just you. Some doors are designed to confuse you.