english: Because if the tile in that shadow were in fact in shadow, and reflecting the same amount of light to your eye as the one outside the shadow, it would have to be more reflective -- just the laws of physics.
non_english: skutočne zatienená, a odrážala by rovnako veľa svetla do Vášho oka ako tá mimo tieňa, musela by byť viac reflexná -- to sú proste fyzikálne zákony.