"There is always a disposition in people's minds to think the existing conditions will be permanent. When the market is down and dull, it is hard to make people believe that this is the prelude to a period of activity and advance. When the prices are up and the country is prosperous, it is always said that while preceding booms have not lasted, there are circumstances connected with this one, which make it unlike its predecessors and give assurance of permanency. The fact pertaining to all conditions is that they will change."
Charles Dow (1851-1902) aplicando Heráclito de Éfeso aos mercados, citado em The Evolution of Technical Analysis.