Renowned behavioral economist Dan Ariely explains why humans are biologically wired to make irrational decisions when money is involved. It’s a case of our evolutionary wiring interfering with the decisions we face in a modern world very different from the one our ancestors adapted to.
For instance, he explains how one of the easiest phenomena to create in a lab are valuation “bubbles”. Our vestigial herding instinct encourages us to imitate the actions of those around us (e.g. bidding for a particular asset), which then strengthens that signal for others (leading to even higher bidding), resulting in behavior not justified by the underlying fundamentals of reality (asset prices destined to crash).