[setr]

Im no economist but intuitively i would think the key piece is that they “pop”; that is, the market corrects itself ib a sudden and aggressive fashion. That its a “correction” necessitates that the valuation is divorced from its “real” value, the primary mechanic allowing this being speculation.

And ofc, since speculation and correction is always a market, the final piece of the dish is that the speculation (and thus, the eventual correction) is significantly large.

And then given that the market itself lasts long (substantially longer than decades), and that we rightfully fear, not the existence of, but the crash, then it seems fine to claim a bubble lasting decades, and even centuries.

And like all predictions of the future, there’s money to be made in the difference between its actual popping and its predicted pop, if you choose to make the bet. Ofc, money to be lost too. And if you expect it to last a century... then just make sure your grandchildren get out before it bursts (and hope it doesn’t take everything else with it). Doesn’t matter to you particularly at that time scale, but it still exists (unless ofc it corrects slowly... but hey, hindsight is 20/20)