They don't reverse left and right. But the relative position from which you look in the mirror can make it seem like left and right are reversed.
Stand in front of a mirror. Use your left hand to touch your left ear. This all happens, in the mirror, on the left side (the left as you see it.). BUT For someone standing just above and behind the mirror, though, they would say that the right side of the mirror showed you touching your ear. Because they, like the mirror, are standing opposite of you.
Relative to you, the mirror has not flipped left to right. Relative to your friend standing above/behind the mirror, and only watching the mirror image, it gets confusing, though. They have to remember that their right is still your left.
Alternative: you're driving along and a siren comes screaming up behind; in your rear view mirror the sign says "AMBULANCE" on the vehicle. But if you turned around to look at the ambulance, the letters are all backwards, from the E to the A. BUT, the letters are not reversed in the mirror. What happens is that when you look in the rear-view mirror you're looking from a different position. Behind your left ear is the letter A -- this ends up on the left side of the rear-view mirror as you look at it. Behind your right ear is the letter E on the Ambulance sign -- this ends up on the right side of the mirror, as it needs to be. All the other letters fall into their right relative places, too.
Stand in front of a mirror. Use your left hand to touch your left ear. This all happens, in the mirror, on the left side (the left as you see it.). BUT For someone standing just above and behind the mirror, though, they would say that the right side of the mirror showed you touching your ear. Because they, like the mirror, are standing opposite of you.
Relative to you, the mirror has not flipped left to right. Relative to your friend standing above/behind the mirror, and only watching the mirror image, it gets confusing, though. They have to remember that their right is still your left.
Alternative: you're driving along and a siren comes screaming up behind; in your rear view mirror the sign says "AMBULANCE" on the vehicle. But if you turned around to look at the ambulance, the letters are all backwards, from the E to the A. BUT, the letters are not reversed in the mirror. What happens is that when you look in the rear-view mirror you're looking from a different position. Behind your left ear is the letter A -- this ends up on the left side of the rear-view mirror as you look at it. Behind your right ear is the letter E on the Ambulance sign -- this ends up on the right side of the mirror, as it needs to be. All the other letters fall into their right relative places, too.