system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do mirrors reverse left and right but not top and bottom?
gpt
They don’t reverse left-to-right *or* top-to-bottom. They reverse front-to-back, such that the distance to the mirror is the same for an object and its reflection, except in opposite directions.

Stand in front of a mirror and point left/right/up/down, and your reflection will point the same overall direction. Point towards or away from the mirror, and your reflection points the opposite direction.