Bloomberg: Twitter CEO Dick Costolo has had a rough couple of years, taking the company through an initial public offering and shuffling his management team to deliver on high expectations of user and sales growth. Last week, Twitter reported revenue that missed analysts’ projections for the first time, causing its stock to plunge. Even as Wall Street scrutinizes his leadership, Costolo is in good spirits. “I’m a big proponent of living in the moment and not thinking too much about where am I going to be two years from now.”