Preface: I first published this article in March 2018. A recent tweet highlighting a 2014 interview with Elon Musk reminded me of it, and since the piece is as relevant today as ever, I'm reposting it below with only minor changes. Enjoy!
I think anyone who has ever played the stock market has considered it irrational, at least some of the time. When a stock goes in the opposite direction from what you expected, that's typically the feeling.