When we count something, we use natural numbers. For example, first, we cut 1 piece of a cake, then we cut another one and we have 2 small pieces of cake. Or we collect apples, we take 1, then another 1, and we have 2 apples. We add numbers to each other using addition. If we use subtraction the same way, at a certain point, we will have to deal with negative numbers.
