> in a ponzi earlier investors are paid from the investments of future investors.

Also, a Ponzi scheme requires fraud, where the earlier investors are being lied-to about where the money comes from in order to paint a false financial picture of the company.

Not directly related to your point, but I wanted to put that out there since it's a pet-peeve of mine that "Ponzi" gets frequently misused as a label for anything the speaker thinks is unsustainable.