system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do car doors have those “checkpoints” when you open them that causes the door to swing back if you don’t get it just right?
gpt
There is a spring-loaded wheel with notches at specific points. It is good at holding the door steady with no effort by you, but the side effect is that it pushes the door *away from* spots between the steady spots.