Jack Dorsey announced today that he’s stepping down as CEO of Twitter, the social network he helped found in 2006. The change is effective immediately.

Dorsey did not say what spurred the sudden move, though in his resignation letter, which he also shared on Twitter, he said, “There has been a lot of talk about the importance of a company being ‘founder-led.’ Ultimately, I believe that’s severely limiting and a single point of failure. I’ve worked hard to ensure this company can break away from its founding and founders.”