Stubborn

Why is it that my son is stubborn about ridiculous things? All my friends' kids try to get their own way about what to buy at the store (all the toys, of course), what to eat (junk food) and what to wear (whatever is inapproproate for the weather and would embarass mom in public). Noah doesn't care so much about those things. He's finds groceries as interesting as Elmo, would much prefer veggies to anything else (so long as it's pureed), and while he went through a naked phase for a few months he seems to be mostly over it. So what does he assert himself over? Shapes. He spent 15 minutes this morning insisting that a square was really a circle. He knows his shapes, so I have no explanation other than he's trying to confuse me. Yesterday he brought me the exact same square cookie cutter and told me it was a "skwuh", but today it's a "suwkuw" and if I say differently it's tantrum time. At first I thought he just wanted a circle, but when I tried giving him one instead that led to a fit too. Would you call a square a circle to avoid a tantrum? I think there's too much teacher left in me or else I might consider it.