PandoDaily
The former improv actor, who served as Twitter's CEO for five years, is stepping down after the company has come under increasing fire for disappointing user growth and financial performance.
The problem, Costolo said in an interview with the Guardian, is that Wall Street is obsessed with the short-term picture.
"You always want to keep focused on the long-term vision, yet when you go public you're on a 90-day cadence and there's a very public voting machine of the stock price that accelerates that short term thinking."
The votes have definitely not been favorable. Shares of Twitter are down roughly 35 percent from their 52-week high.
Costolo took the social media company public and helped develop its advertising business. He noted in the interview that the service was still suffering from regular technical outages when he started, something that is no longer the case. And he said that the company has stuck to a "cohesive long term strategy" which includes many of the features that are gradually rolling out, including a new focus on live events such as sports.
Twitter co-founder Jack Dorsey starts on Wednesday as Twitter interim CEO - he'll be doing double duty with his other full-time day job as the CEO of payment company Square. Twitter's board meanwhile, is on the hunt for the company's next permanent CEO.