Well, gosh, your life is meaningless drivel unless you fill those boxes with stuff! Produce! Nevermind what your wife and kids think of you, nevermind the laughter of your friends, the beauty you saw, the wonders you imagined. All those times you helped out a bum, cooked dinner, played with your niece: meaningless, if it got in the way of putting an achievement into a month-box! Produce! Produce! What are you going to have to etch on your tombstone if you don't have a dozen github URLs?

I think that's the point. It doesn't matter what you fill them with--fun, work, standing on your head--just that you feel accomplished by having done what you've done. If you don't, then maybe it's time for some change.