والشمس كالمرآة في كف الأشل
And the sun is like a mirror in the palm of a person with an impaired hand.
The point is not merely that both the sun and a mirror shine. The particular condition of the impaired hand contributes instability, movement, or a changing reflection to the intended image. Several visual features must be assembled before the resemblance becomes apparent.
A simple mirror can suggest an ordinary likeness. A mirror under this special condition requires an additional mental step. Such qualification can move the comparison toward the remote and uncommon.