That you cannot lie about how many bitcoin there is or will be. As money is some kind of base layer of civilisation, a fundamental communication layer between people that know and don’t know each other, dealing with goods and services, it is of great importance that you cannot distort the communications layer by injecting more of the money into the system in a devious way….in other words that you’re not permitted to lie to give yourself unwarranted benefits.

The proof of work is the mechanism by which bitcoin enforces this truth. I think this is the answer to your question.