I proved that since I had to redo the upper half FOUR times (!) before I was happy with the result (the hat kept being too short, and I had yarn left over). Every time, I had to open the hat up to the point where I started decreasing stitches, so that I could add a row or 2 (2.5 in the end), and see whether the final product reached past the ears! :) Man, oh man, if one has nothing better to do, eh?
I particulary like the spiral pattern on the top!