I think in every case, some risks are underestimated. Shiller may consider it questionable investor learning.

Sure-win mentality breeds the gambler behavior

eg: Is SP500 ETF a sure-win? Many American investors seem to feel that way.

eg: Is DIVA an arbitrage, sure-win?

eg: Q to H.Luo : Is Singapore condo a sure-win? I think many investors use maximum leverage to invest in Singapore condos. Sure-win due to Ponzi nature. https://tanbinvest.dreamhosters.com/26043/sg-home-buyers-max-out-mtg-quantum/

— Single stocks:
eg: Is Singapore IPO sure-win? This was one of my first “sure-win” bets.
eg: when Singtel shares were offered to the lay public, some probably considered it a sure-win. Utility stock backed by government.
eg: in 2020, my wife picked SIA as a sure-win stock.