All bubbles pop--and not just stock market bubbles. A speculative bubble is a psychological-social phenomenon in which confidence in the stability of future gains reaches levels where doubts are banished and risks have dissipated into thin air. This confidence can be euphoric or it can be the baseline: this (guaranteed gains) is the way the world works.
This baseline confidence in the system is a form of received wisdom based on recency bias: since gains keep notching higher, the evidence supports expectations of future gains. Thus embracing what is clearly over-confidence (i.e. a bubble) is perceived as rational, and doubting future gains as irrational.
For example, the Higher Education Bubble is popping. The PR machinery that generated the confidence that borrowing immense fortunes to pay for university diplomas was a means to securing guaranteed lifetime gains is breaking down.
This confidence was not euphoric, it was received wisdom based on recency bias: study after study showed those with any flavor of four-year college degree earned far more over their lifetimes than those with only high school diplomas.
https://charleshughsmith.substack.com/p/all-bubbles-pop