If you've never picked up a zonked out 4 year old whose been near comatose for roughly 45 minutes, carried him up a flight of stairs, and then stood him in front of the toilet to pee (STILL asleep, mind you) you're gonna have to trust me:
It ain't as easy as it sounds. Throw in basic physics, a little geometry, and 4 Hail Mary's and you get the idea.
Best part? Like an athlete who has trained his muscles to give the exact same swing every time, he actually reached forward to drop the lid down after he finished.