Nothing so gives the illusion of intelligence as personal association with large sums of money.
The circumstances that induce the recurrent lapses into financial dementia have not changed in any truly operative fashion since the Tulipomania of 1636-1637. Individuals and institutions are captured by the wondrous satisfaction from accruing wealth. The associated illusion of insight is protected, in turn, by the oft-noted public impression that intelligence, one’s own and that of others, marches in close step with the possession of money. Out of that belief, thus instilled, then comes action – the bidding up of values, whether in land, securities, or, as recently, art. The upward movement confirms the commitment to personal and group wisdom. And so on to the moment of mass disillusion and the crash. This last, it will now be sufficiently evident, never comes gently. It is always accompanied by a desperate and largely unsuccessful effort to get out…
There is nothing in economic life so willfully misunderstood as the great speculative episode.
— John Kenneth Galbraith 1908 – 2006, A Short History of Financial Euphoria