The feeling that mirrors reverse left and right comes from how humans imagine reflections as rotated people.

We tend to think of the mirror image as another person standing opposite us, facing us after turning around. When a person turns 180 degrees, their left and right sides switch places compared to us. But a mirror doesn't actually rotate the image; it just flips front to back. Our brains interpret the mirror image as if it had been rotated, which causes the illusion that left and right are swapped. The symmetry of the human body — which looks very similar left to right but different front to back — adds to this confusion.