The vacuum cleaner story made me think of a time when two supposedly smart adults were standing in front of a car trunk trying to figure out how to squeeze in a child's bike, having already tried several times and failed. DD (I believe she was 7 then) came up, looked at it, and said "Why don't you turn it around the other way and put the handlebars like this and put it like that?" (gesturing to make her point) Other adult: "Oh, I don't know." Me: "No, she's probably right." She was.