self-contained-economy

This concept was pointed out by the developer of Axie Infinity game.
I think this is the core-value success of any P2E game.

Player must do some form of action or work to create value. And these value must be used in this same economy. Either by consuming themselves or give to another player that want to join this economy.

Aka the same mechanic as proof of work/proof of play, do some energy work for token. It was the trust that have value outside of the closed economy. For this game, it have extra enjoyment value.