Benjamin Graham on Mr. Market
Common stocks have one important investment characteristic and one important speculative characteristic. Their investment value and average market price tend to increase irregularly but persistently over the decades, as their net worth builds up through the reinvestment of undistributed earnings. However, most of the time common stocks are subject to irrational and excessive price fluctuations in both directions, as the consequence of the ingrained tendency of most people to speculate or gamble.