The Psychology of Speculation by Henry Howard Harper

When the whole country becomes pervaded with an epidemic of bullishness / the action of speculators is always directed by sentiment rather than / judgment; and a market that is swept along by excited emotions is / always dangerous, -- dangerous to go short of and dangerous to be long / of. Hysterical "bulls" care nothing whatever about the earnings or / dividend returns on a stock; the only note to which they attune their / actions is the optimistic slogan, "It's going up! " and the higher it / goes the more they buy, and the more their ranks are swelled by new / recruits. A herd of stampeded cattle (cows no less than bulls) will / rush blindly into a river, or butt their brains out against stone / walls, trees or other obstructions; they also stampede every critter / that happens along their path; and anyone who has ever witnessed a / panic in a theater or auditorium, or in the stock market, need not be / told that under such circumstances men are but little saner than cattle.

And speaking of sentiment, it is remarkable to what extent the combined / business and financial structures of the country are swayed to and fro / by this giant motive power. Like the biblical wind that bloweth where / it listeth, and man heareth the sound thereof but knoweth not whence it / cometh or whither it goeth, sentiment springs up from comparatively / trifling or unknown sources and after playing its havoc, vanishes as / suddenly and mysteriously as it came. In a bear market a train wreck, / or the death of some financier, or an earthquake in Europe, will put / the market off to the aggregate extent of hundreds of millions; whereas / one of the greatest bull markets in history found its chief impetus in / the most universally devastating war the world has ever known.