I’ve made my share of mistakes while investing that ended up as expensive lessons. In this article, I share one particularly painful mistake and three lessons that I took from it. What Happened? In October 2015, I bought shares of Chipotle Mexican Grill Inc (NYSE: CMG). At that time, Chipotle’s share price had fallen 25% from its peak following a Salmonella outbreak at one of its outlets. As such, I managed to pick up shares at US$565 per share, compared to the previous high of US$749. I had been eyeing Chipotle for some time and thought that it was a great opportunity to buy shares. Chipotle was a fast-growing fast-casual restaurant chain in the US that still had a huge market opportunity to expand into. Its food – Mexican fare- were popular and its comparable sales stores were consistently in the mid-to-high single digits or higher. The company was ambitiously expanding its store footprint in North America....