The investor has the benefit ...

The investor has the benefit of the stock market's daily and changing appraisal of his holdings, 'for whatever that appraisal may be worth', and, second, that the investor is able to increase or decrease his investment at the market's daily figure - 'if he chooses'. Thus the existence of a quoted market gives the investor certain options which he does not have if his security is unquoted. But it does not impose the current quotation on an investor who prefers to take his idea of value from some other source.
 Benjamin Graham

Quotes from the same author

The volume of credit depends upon three factors: the desire to borrow, the ability to lend and the desire to lend.
 Benjamin Graham
It is no difficult trick to bring a great deal of energy, study, and native ability into Wall Street and to end up with losses instead of profits. These virtues, if channeled in the wrong directions, become indistinguishable from handicaps.
 Benjamin Graham
The reader can test his own psychology by asking himself whether he would consider, in retrospect, the selling at 156 in 1925 and buying back at 109 in 1931 was a satisfactory operation. Some may think that an intelligent investor should have been able to sell out much closer to the high of 381 and to buy back nearer the low of 41. If that is your own view you are probably a speculator at heart and will have trouble keeping to true investment precepts while the market rushes up and down.
 Benjamin Graham
The individual investor should act consistently as an investor and not as a speculator. This means ... that he should be able to justify every purchase he makes and each price he pays by impersonal, objective reasoning that satisfies him that he is getting more than his money's worth for his purchase.
 Benjamin Graham
It is absurd to think that the general public can ever make money out of market forecasts.
 Benjamin Graham