Marks' memos, which he has written since 1990, have long been priority reading for some of the best investors in the world -- Warren Buffett has famously said that whenever he sees one in his inbox, that's what he reads first. In 2011, Marks released his first book, The Most Important Thing, which, in direct contradiction with the title, listed 20 things to which the successful investor ought to pay attention. His second book, out this month, is titled Mastering the Market Cycle: Getting the Odds on Your Side. As you say, it's not science. It's not numbers. It's not formulae. It's understanding developments in the real world, how they occur, and how the elements combine to produce those cycles. Only by having an appreciation for the workings of these things -- and not by expecting to be given a formula that you can plug and play -- can investors perfect this essential skill. Marks: So the improvement has to be intentional, and the first thing you can learn is why it's important to be unemotional and why emotionality is the enemy of the investor. Why human emotion conspires to constantly make investors do the wrong thing. Well, No. 1, a lot of the companies to which nothing bad could happen had bad things happen. So much for predicting the future. But No. 2, because the companies were so highly rated, they were extremely highly priced, and if you joined when I did in 1968, and you bought those 50 stocks, and you held them diligently for five years, you lost almost all your money. https://www.fool.com/investing...