Equal units ≠ equal parts
Everybody forgets the 27th mile. Sure, a marathon is technically only 26.2 miles, but a lot of folks just round down to 26. They shave off that last two-tenths, because they think it won't be much, because they think it's just a tack-on.
But it's not.
I just finished my fourth marathon in two months, and having done this last little bit four times recently, I can tell you it's no tack-on. By the time you get to the end of a marathon, every step is heavy, hurts, hammers you into the pavement. No matter what your pace or ability, you're beat by the end. Mashed potatoes, emphasis on "mashed."
If you break down the 26.2 miles of the marathon into equal units, each two-tenths of a mile, you get 131 little units of distance. But I assure you, that 131st unit is exponentially more difficult than the 1st, 50th, or 100th. Equal units is not equal parts!
You'd expect that, even if you're not a runner. Of course that last little bit is tough. But I don't think we apply the same thinking in other tasks. We tend to think of the end of a project or a written work or a personal objective as equivalent to the things that came before.