Except in passing, I have never had much interest in crypto - belonging in the too difficult to understand bucket.

But I came across this article (reddit) I find fascinating. Ponzi?

The cryptocurrency ecosystem is conceptually simple. Money comes in from new investors buying, and the same money comes out to pay those cashing out. It would be a zero-sum ecosystem, except for the fact that miners have to pay their bills in dollars

This is why "bitcoin investors" feel an immediate urge to tell everyone else to invest in bitcoin -- if no new money comes in, the financial structure eventually collapses under the miner's sell pressure.