system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why was the discovery of zero (or the lack of a concept of zero) by ancient civilizations such a big deal?

I read things like that zero was invented independently in Mesopotamia and Mesoamerica, or that the Romans didn’t have a concept of zero.

What does it really mean to have “discovered” zero, and what was made possible that was impossible before?
gpt
It just sort of wasn’t a concept before then. Like, people knew what having 1 apple was like, or having 2 apples, or 3, etc… but no one really thought to define a number that represents “no apples”. If you have no apples, you don’t need to describe the number of apples you have because there are none to describe. 

But then someone decided, hey, you know what? It might be useful to have a number that represents nothing. They just sort of decided to make it a thing, and then followed through on the logic of what having a zero meant. Turns out, it’s a very useful idea that extends to way mole than just whole numbers, and allows for much more complicated math. 

But yeah. There wasn’t anything preventing people from having a zero other than just people not thinking they needed a zero.

**Edit:** *That’s a response to the body of your question, but as for the title, zero is just a really useful concept. It showed a precedent for negative numbers, irrational numbers, complex numbers and quaternions by extending our concept of numbers to beyond what we first though they were. The idea of approaching zero is fundamental to the creation of calculus, and a zero is needed to define vector spaces. Basically none of modern math would be possible without zero.*