A $1.6 trillion investment chief shares the biggest lessons that guide him through erratic markets

The stock market this week had its biggest decline since the United Kingdom voted to leave the European Union in June 2016.  Such moves, and worse, are familiar to Tim Armour, the CEO of $1.6 trillion asset-manager Capital Group. "The most important lesson I’ve learned over time is that you have to contain your emotions," he said.  "Keep calm and carry on" is not exactly the kind of temperament traders are inclined to have when the Dow Jones industrial average is down by over 1,000...