The reason prices can be rational and euphoric at the same time

During a boom, every buyer had a reason: the trend was strong, the narrative was compelling, the opportunity was visible. Each trade, taken alone, was defensible. But the sum of all defensible trades produced a price far beyond any fundamental anchor — a bubble no single participant meant to create. The market was not irrational participant by participant; it was irrational in aggregate, because individually reasonable decisions, made by people responding to each other’s actions, compounded into an outcome none of them separately would have endorsed.

What everyone sees

A participant sees his own decision as rational — he has reasons, he has a thesis — and reads the market’s strength as confirmation that others are equally rational. The word bubble feels wrong because nothing he personally did was unreasonable. The participant does not see that the aggregate of many individually rational responses to the same signals produces an emergent irrationality that no single actor caused or can prevent.

What is actually happening

Research on emergent properties in financial markets shows that individually rational actions can aggregate into collectively irrational outcomes, a phenomenon formalised in models of rational herding and information cascades. Each participant responds sensibly to the signals available — including the price moves created by previous participants — but the sum is a self-reinforcing spiral. The bubble is not made of irrationality; it is made of rationality applied to a reflexive system where each person’s rational action alters the signal the next person sees.

Why it stays hidden

The hidden mechanism is rational individual behaviour aggregating into an irrational collective outcome through reflexive feedback. Each buyer is right given what he sees; what he sees includes the buying of others; and the sum of all right-given-what-they-see decisions is a price that is wrong by any fundamental measure. The euphoria is an emergent property, not a personal failing, and that is what makes it invisible from the inside.