Why strive to get 4 zeros in the hash for a block?

Question

blockchain

I can not calm myself, why these 4 zeros? If all blockchain communication is as reliable without reaching 4 zeros.

Answer 1

not why but why, zeros in the hash is an artificial task (simple and at the same time requiring energy to solve, since it needs a blunt enumeration to solve it), the complexity of the solution of which is easily adjusted to the required one (depending on the current power of all miners) such so that the time to find the next block is approximately the same
ps not 4 but the required amount