One of the most awesome truisms I ever found is: you REALLY
   don't understand something unless you can teach it to someone
   else and they 'get it'. It's cliche for a good reason - it's
   really true. A little related thing that never ceases to amaze
   me: No matter how many ways we try, we can never see the 8th
   corner of a solid box. Lacking multiple perspectives, we have to
   imagine the 8th corner. Even babies deal with these kinds of
   mysteries in their own fashion - imagining the unseen.