A bubble that pops is caused by an event that triggers a panic wherein people are looking to sell and are happy to reduce their price of selling sharply in order to dispose of an asset.

The question we have to ask is - what event will trigger this? To the extent that marginal investors (who who are price makers) will seek to exit.

The thing is, the “event” can be as simple as normal market fluctuations, because once idea of a potential bubble becomes sufficiently widespread, any momentary downturn in any indicator will be seen by some segment of the market as a sign that the burst is here, and if that segment is large enough, it becomes a self-fulfilling prophecy.