This blog's content was taken from episode 303, "Businesses That Provide Monster Returns (100x Stories with Chris Mayer)"

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In the start of Chris Mayer's book he discusses the coffee can portfolio concept. The coffee can portfolio came from a guy named Robert Kirby, who wrote about it in the Journal of Portfolio Management in 1984. 

Kirby was a money manager, and he had an interesting experience where he was managing a woman's money for years. Unbeknownst to him, her husband had been piggybacking on all his ideas, except with one change, which was he never sold anything. Years go by and the husband dies and he gets the account. That is when a woman transfers the account to him, and that's when he sees this man has been buying all this stuff that he's bought for her over the years. Some of the positions had become monsters, including one that was bigger than the entire portfolio he managed for her. In the end it hit him that it was a lesson, there is too much turnover and he would have been better off had he not been so active. So he came up with this idea which he called the coffee can portfolio. 

The idea of the coffee can comes from, in the old West, people used to put their valuables in an empty coffee can and they would hide it and leave it alone. So that idea would be applied to portfolio management. You are creating a portfolio with a smaller amount of stocks that are carefully chosen, put it in your coffee can and leave it alone and see what happens. 

It forces you to really think long-term because you know you're not going to be able to sell something. As well, it protects you from your worst instincts, selling when stocks are down or chasing things that are hot. The concept is great because you're forced to try to at least pick companies that you know are going to have some sort of enduring competitive advantage because you can't do anything. You can't change names in and out of the portfolio.