Why did people invent zero?

Here is a strange thought: for thousands of years, humans counted everything around them — sheep, jars, stars, grandchildren — and never once needed a number for nothing. Why would you? You don't count the goats you don't have. And yet, one day, somebody decided that nothing deserved its own number. That somebody invented zero, and it quietly changed the world.
To see why zero took so long, picture an ancient shepherd. He has five sheep, so he scratches five marks on a stone. Easy. But when all the sheep are gone, what does he scratch? Nothing! He just doesn't make a mark. For everyday counting, "nothing" never needed a symbol — it was simply blank.
