A few years ago I met Jose Gabrielli, the CEO of the Brazilian energy giant Petrobras, to talk about an article we were developing for HBR. Dressed in a dark suit and tie, I entered his office on a top floor of the company’s monolithic building in downtown Rio to set up for our interview. Then in walks the man, the head of a $100 billion multinational, wearing blue jeans, a photo ID dangling around his neck. It was casual Friday.