Page "Economic bubble" Paragraph 18

While there is no clear agreement on what causes bubbles, there is evidence to suggest that they are not caused by bounded rationality or assumptions about the irrationality of others, as assumed by greater fool theory.

It has also been shown that bubbles appear even when market participants are well-capable of pricing assets correctly.

Further, it has been shown that bubbles appear even when speculation is not possible or when over-confidence is absent.