How come market values generally reflect intrinsic value?

I thought the quote below by Ben Graham would be informative; or at least would make us feel better about not understanding the stock market.

It's taken from a superb biography on Warren Buffett by Roger Lowenstein (which I highly recommend, by the way). Warren Buffet himself learned the basics of investing from Ben Graham, then Professor at Columbia and co-author of the classic book Security Analysis.

Graham was invited to testify in congress in the mid-50's because of fears of another bubble like that of 1929. The quote is as follows:

Chairman: When you find a special situation and you decide, just for illustration, that you can buy for 10 and it is actually worth 30, and you take a position, and then you cannot realize it until a lot of other people decide it is worth 30, how is that process brought about–by advertising, or what happens?

Graham: That is one of the mysteries of our business, and it is a mystery to me as well as to everybody else. But we know from experience that eventually the market catches up with value.