One drop of water can go a long way, but he hasn’t always followed each one to the end. He just assumed he could tell where each one would end up, because surely one drop of water didn’t matter so much in the big picture, right?
But if he were right, he wouldn’t be sleeping with a branch for his pillow every night. If he were right, then he’d have to admit that whatever he did or does or will do would never matter in the long run, because like a rolling tear, there’s just no way to tell how significant he or anyone else is. They were all sand; all sheep; all dust sifted into the wind, but only some are picked by the hands of choice and fate, and no one but the one who knows the future can tell.
So he turns around before he can roll too far, and decides that judgement is something he doesn’t have the right to reserve.