It's how people count things. If you want to know how many sheep or apples are in front of you, you start counting at one, and the number you get up to is the n

It's how people count things. If you want to know how many sheep or apples are in front of you, you start counting at one, and the number you get up to is the number that there are. If there are i elements of a set, the first element is the 1st element and the last element is the ith element. Doing it otherwise risks fencepost errors. (There are perfectly reasonable arguments why computer languages might be zero-indexed, whereby objects start at the zeroth offset. But counting from 1 upwards is definitely more natural for counting, it's disingenuous to pretend otherwise).