1. peter_k says:

Because if we take any 2 subjects, then take 2 more subjects and recalculate what happened, we get 4. The laws of mathematics reflect the real world.

2. aqua_altynai says:

Because 2 is a symbol that denotes, for example, 2 objects, 2 people, etc. And the number 4 is also a symbol, only already denoting 4 objects, 4 people, etc. 2+2=4. That is, 4 is a composite number, which can be divided not only by itself and 1, but also by 2. So, if you take 2 items and add 2 more items to them, you get 4. This is a law of mathematics and logic.

3. anna_samolyuk says:

Well, maybe because it's a law of mathematics? There is a certain order of numbers, which was invented and now we all use it. So to think about it, if we just count 1 2 3 4… to get the next number, we add 1 to the previous one, so 1 is the smallest natural number: 1+1=2, 2+1=3, 3+1=4… accordingly, if we add not 1, but 2 to the previous number (2), then we get not 3, but the next 4.

Here's something like that. I think you knew this yourself, but you asked the question just because you had nothing better to do…