I remember that they [Ev and Biz at Twitter in 2008] very firmly believed spam was a concern, but, “we don’t think it's ever going to be a real problem because you can choose who you follow.” And this was one of my first moments thinking, “Oh, you sweet summer child.” Because once you have a big enough user base, once you have enough people on a platform, once the likelihood of profit becomes high enough, you’re going to have spammers.