I took a graduate level measure-theoretic probability theory class. The professor had this rant about how "buy low, sell high" was a bad idea, it's all about ho

I took a graduate level measure-theoretic probability theory class. The professor had this rant about how "buy low, sell high" was a bad idea, it's all about how long you stay in the market. He had a mathematical proof that, if I recall correctly, only held if the random process is monotonically increasing in expectation, which of course is not guaranteed.