The initial spark that showed Calm co-founders Alex Tew and Michael Acton Smith there was a market for meditation was rather simple. Tew, who had become a minor internet celebrity for the Million Dollar Homepage, built a website in 2011 called ‘do nothing for two minutes’, in which a user would stare at a screen and listen to waves on a beach for two minutes without touching their mouse. At the end of two minutes, an email prompt would appear asking people to sign up. In two weeks, over 1...