When they find a cheap stock, they may start to buy even before they have completed their research. They have at least a rudimentary knowledge of thousands of companies, and they can consult Value Line or the S&P stock guide for a quick check into the company's financial position. Both believe that the only way to really know a security is to own it, so they sometimes stake out their initial position and then send for the financial statements. The market today is so fast moving that they are almost forced to move quickly.

(Bruce Greenwald about Walter and Edwin Schloss)

That's an interesting approach. I agree that the only way to really know a stock is to hold it for a while. But only a truly experienced investor can get away with incomplete research. Opportunities do vanish quickly, yet modern technology lets you track a big watchlist, so new ones keep coming. I prefer to finish my research, sleep on it, and buy after that.