(with a little help from physicist Richard Feynman as quoted in James Glick's book Genius)
"Imagine yourself standing before a mirror with one hand pointing east and the other west. (Notice we are not using the terms left or right.) Wave the east hand. The mirror image waves its east hand. Its head is up. Its west hand lies to the west. Its feet are down. Everything's really all right. The problem is on the axis running through the mirror. Your nose and the back of your head are reversed: if your nose points north, your double's nose points south. The problem now is psychological. We think of our image as another person. We cannot imagine ourselves 'squashed' back to front, so we imagine ourselves turned left and right as if we had walked around a pane of glass to face the other way. It is in this psychological turnabout that left and right are switched. It is the same with a book. If the letters are reversed left and right, it is because we turned the book about a vertical axis to face the mirror. We could just as easily turn the book from bottom to top instead, in which case the letters will appear upside down."
Now go and never again say your image is reversed.