Money can only be solid, hard money when coupled with the marginal cost of its creation. It's called Proof of Work because governments, kings and politicians have always lied to the people with every other monetary principle sooner or later.

"The adjective “precious”—referring to the fundamental limit on availability established by what a massive pain in the ass it was to find and dig up the intrinsically scarce commodity out of the ground—was important, because, well, everyone cheats: the buyer in the marketplace shaves down his metal coin and saves up the scraps, the seller in the marketplace weighs the metal coin on dishonest scales, and the minter of the coin, who is usually the regent, or the State, dilutes the preciosity of the coin’s metal with lesser materials, to say nothing of other methods." Edward Snowden

(“Your Money AND Your Life,