"Long before the Twitter revolution and his ascent to the heights of social media, Mr. Costolo was a professional comedian. And you know what? He’s still doing improv — only it’s the business kind. He’ll wax on about growth and revenue like the next C.E.O. But then he’ll dig out a joke and do something that might hurt his business — and miff his investors — because, well, he thinks that something is the right thing to do."