I don't agree with you stefano...
Take a mirror on the wall for instance and look from closeby at the surface of the mirror. The mirror itself is then "in focus". Meaning that you can see little scratches and imperfections on the surface of the mirror.
On the other hand... The reflection of the mirror is still at a distance and you can't get that one sharp unless you focus on it (but then you will lose the focus on the surface of the mirror)