Undervaluations caused by neglect or prejudice may persist for an inconveniently long time, and the same applies to inflated prices caused by over-enthusiasm or artificial stimulants.
Benjamin GrahamExperience teaches that the time to buy stocks is when their price is unduly depressed by temporary adversity. In other words, they should be bought on a bargain basis or not at all.
Benjamin GrahamPrice fluctuations have only one significant meaning for the true investor. They provide him with an opportunity to buy wisely when prices fall sharply and to sell wisely when they advance a great deal.
Benjamin GrahamWe have been trying to point out that this concept of an indefinitely favorable future is dangerous, even if it is true; because even if it is true you can easily overvalue the security, since you make it worth anything you want it to be worth. Beyond this, it is particularly dangerous too, because sometimes your ideas of the future turn out to be wrong. Then you have paid an awful lot for a future that isn't there. Your position then is pretty bad.
Benjamin Graham