The zeroth law of P2E games

What's the most important rule for play to earn games? 

In the previous episode I talked about what could be called "the first law of P2E games", or perhaps "The fundamental theorem of P2E economics", but Mark Skinner pointed out to me that there is a more important one:  The zeroth law of P2E games. And it doesn't just apply to P2E.  What that is, is revealed in the episode.

It's so obvious a lot of people forget about it.