The Reference Desk/Why was The Doctor not affected by the crack in the wall's light?

In Cold Blood, The Doctor reaches into the crack in the wall in the Silurian area and pulls out a piece of the exploding TARDIS. But when light from this same crack hits Rory Williams, he is erased from existence.

How could The Doctor reach into the crack and be perfectly fine while Rory completely disappeared as if he never existed?