Every principle has a material counterpart. Two eyes for two hemispheres. A 'processing center' as third component to combine information.

The magic isn't in the wand or the one who waves it.

The magician has a weak understanding of the forces he fears and desires to control them, most always as a force against another entity or object. The literalist is doomed to such a fate, especially when positing the 'third eye' merely as a gland that resides in the head. The placement Between the eyes is a key to the mystery that goes beyond any physical explanation.