Nat Friedman was on a 6 month trip around the world with his wife. But he cut his trip short so he could fly back within 48 hours to start Xamarin. Miguel de Icaza, his co-founder, told him there was a chance to own the Mono framework and apply it to mobile enterprises as part of a standalone company. When an idea grabs you, there is no notion of later. The time is now.
While most people believed .NET was a dead language, they ignored the fact that there were 6-8 million Windows developers worldwide who needed powerful tools to create mobile apps. While everyone was talking in terms like Ruby on RAILS, PHP, Python, and Cocoa, team Xamarin had the contrarian insight to solve a problem that was immediately top of mind to a massive group of developers.