I’m not sure I agree with that definition of bubble. I think it’s more like “an investment whose cash inflows are primarily driven by a feedback loop of highe

I’m not sure I agree with that definition of bubble. I think it’s more like “an investment whose cash inflows are primarily driven by a feedback loop of higher prices and greater investment” — that is, investors’ motivations are detached from any NPV-like evaluation of the investment. We really only know it’s a bubble after it pops. Before that it’s maybe less prejudicial to call it a speculative market.