Ponzis are so convincing to many because people do profit from them. To them, that's the proof that it's not a scam. And yeah, they work, until one day they don't. It's like the column of ash and smoke from an erupting volcano. It supports itself and continues reaching to the sky so long as the eruption from the volcano continues supplying more ash and smoke to keep it up. And hey, as long as it stays up there, everything looks like it's gonna be okay. But when the eruption is complete, the fuel keeping up that column disappears and the whole thing comes crashing down, taking out everything around it as it falls and spreads... like Pompeii.