Why is it we are always forced into a box?

Why is it that when we want to do something new that we have to fit all of that into the pre-made box or constraints. I really want to do standards based grades this year. I have my standards. The big issue is communicating that to a student and parents while boiling learning down in to a number or letter grade. I don't mind being creative to fit into the box but it would be nice not to be crammed into the box in the first place.