When light rays from an object strike a flat mirror, they obey the law of reflection. This law states that the angle of incidence (the angle at which the rays hit the surface) is equal to the angle of reflection (the angle at which the rays bounce off the surface).
Due to this, the light rays that bounce off the mirror and reach our eyes form an image that has the same height and width as the actual object. The only difference is that the image appears to be flipped horizontally (left-to-right) compared to the original object.
This explains why we see ourselves as the same size in a mirror, with the reversed orientation. The reflected image accurately preserves the dimensions of the object, maintaining the size relationship.
