No one had ever explained that to me! 😱😱

That strange, upside-down outlet on your wall might not be a mistake.
It could be a silent signal about how your home was wired, and why your lights behave the way they do.
In many bedrooms and living rooms, a flipped receptacle is the only clue that a wall switch controls the power.

In many homes without original ceiling lights, builders used a switched outlet as the main room light source: plug in a lamp, flip the wall switch, and the room illuminates.
To make that easy to spot, some electricians flip the receptacle so the ground hole is at the top, using orientation as a visual cue.