This week Instagram announced it had reached 300million monthly active users, putting it ahead of Twitter and its 284million users.
Fortune journalist Erin Griffith asked Twitter co-founder Evan Williams about it being overtaken by Instagram, which was bought by Facebook for $1billion in 2012.
His response: "I don't give a shit."
He said that Facebook had convinced investors that the most important metric was total number of users, but he firmly believed what mattered most was user engagement.
If you think about the impact Twitter has on the world versus Instagram, it's pretty significant. It's at least apples to oranges. Twitter is what we wanted it to be. It's this real-time information network where everything in the world that happens on Twitter - important stuff breaks on Twitter and world leaders have conversations on Twitter. If that's happening, I frankly don't give a shit if Instagram has more people looking at pretty pictures.