OK, so I copied this out of Viz, and already told Richard, but its an awesome problem which really shouldn't be hard :P I'm paraphrasing, but it was from the letters page and it went like this

If mirrors reverse everything, why doesn't it look like I'm moonwalking when I walk past a mirror?

A letterbocks pencil for the shortest, most clear answer*

*Offer of prize is for entertainment value only

A mirror doesn't reverse everything, if you put your right hand up in front of it you'll still see it being at your right, the only thing that's changed is depth, which then changes the handedness, in the same way that a reflection changes the orientation in the plane.

Thanks for the letterbocks pencil

What he said ^^ (Please note the shortness and clearness of my answer)

Because you're sh*t at walking.

Our natural definition of left and right is contingent on our definition of forwards and backwards. Whatever is forward: right is 90 degrees clockwise to it, and left 90 degrees anti-clockwise: thus a mirror, which only reverses depth, appears to reverse left and right, when in fact it does not. Our mistake is to empathise with the man in the mirror, and judge his left and right by our own standards when his clockwise can only be our anti-clockwise.

You've made it sound a bit like there's a "trick of the mind" going on, when all it comes down to is the image being reversed due to the light reflecting off the mirror... there's no "why" it's simply "how".

"Why" is always a more interesting question than "how". "How" is for the engineering department to answer.

'Sides, the question asked was a "why".

why is for the philosophy department to answer.

Why are we even answering this at all then?

Oops, thats another philosophy department question.

It's pretty much just like cheese falling off a cliff. You reverse the orientation that way.

Because the mirror only reverses spacial dimensions, not time. Easy.