The ignorance of even the best-informed investor about the more remote future is much greater than his knowledge, and he cannot but be influenced to a degree which would seem wildly disproportionate to anyone who really knew the future, and be forced to seek a clue mainly here to trends further ahead. But if this is true of the best-informed, the vast majority of those who are concerned with the buying and selling of securities know almost nothing whatever about what they are doing. They do not possess even the rudiments of what is required for a valid judgement, and are the prey of hopes and fears easily aroused by transient events and as easily dispelled.

John Maynard Keynes (1883-1946) English economist
A Treatise on Money, Vol. 2 (1930)