It certainly is and your brain actually consumes alot of calories when it's really working hard.

I can't figure out if our creative muscles are so atrophied from fiat world putting us through the cookie cutter or is creativity actually just a fleeting thing.

Seems like when I'm really creative maybe only spend 10% of the day actually making break throughs and the rest is scrap work.

I don't think it's possible to be creative 100% of the day.