At a sleepover with four friends, someone knocked over and smashed a lamp in the spare room while messing about. When your friend's mum came up and asked what happened, everyone went silent, then someone said "we don't know, it just fell." You were all part of the messing about. You don't even know for sure whose elbow did it — maybe yours. So the group story becomes "it just fell on its own." The mum looks unconvinced but lets it go. Now there's an agreed lie holding the room together, and you're part of it. Nobody owned up, including you. "It just fell" is sitting there, and you all know it didn't.