It’s hard to imagine life without WhatsApp, but luckily, Jan Koum, a Ukrainian immigrant to the USA, came up with the communication app in 2009. Despite being born into poverty, Koum developed advanced computer skills from a young age. By 18, he was already highly proficient and landed a job as an infrastructure engineer at Yahoo! in 1997. The idea for WhatsApp came to him after he purchased his first smartphone and realized there was a need for a product that could facilitate messaging between mobile phones, regardless of the user’s location. The app was an instant hit, and Facebook ultimately acquired it for a whopping $19 billion. Koum’s advice for success is simple: “Do one thing, and do it well.”