Chris Day’s first Twitter post was fairly standard. “It feels good to tweet,” he wrote. He got two likes. A week later he posted a second time, about a legal challenge to protect junior doctors’ whistleblowing rights. Hundreds of people retweeted it. Soon, he marshaled an “army” of 3,000-odd backers, who chipped in more than £200,000 ($256,000) to his cause. In 2016 the government wrote the right into junior doctors’ contracts. It really did feel good to tweet.