Deciding based on guesses or emotions

"If we start deciding, based on guesses or emotions, whether we will or won’t participate in a business where we should have some long run edge, we’re in trouble. We will not sell our interested in businesses (stocks) where they are attractively priced just because some astrologer thinks the quotations may go lower even though such forecasts are obviously going to be right some of the time. Similarly, we will not buy fully priced securities because “experts” think prices are going higher. Who would think of buying or selling a private business because of someone’s guess on the stock market? The availability of a quotation for your business interest (stock) should always be an asset to be utilized if desired. If it gets silly enough in either direction, you take advantage of it. Its availability should never be turned into a liability whereby its periodic aberrations in turn formulate your judgments. A marvelous articulation of this idea is contained in chapter two (The Investor and Stock Market Fluctuations) of Benjamin Graham’s “The Intelligent Investor”. In my opinion, this chapter has more investment importance than anything else that has been written."

[Warren Buffett in Buffett Partnership Letters to his partners in July 12,1966]