I think that's especially true for people who, like WhatsApp, do things that are different than the common wisdom [1]. I had dinner recently with a friend who worked for Jeff Bezos years ago. She remembered Bezos coming into a meeting in something like 1999 excited about eInk and how it was the future for electronic books. Everybody single person in the room thought he was crazy. They didn't get the Kindle out the door until 2007, and most people thought it was crazy then. But it worked.
You could call that pure luck, but I think that's only true in the most abstract sense, where everything we are is luck.
[1] http://sequoiacapital.tumblr.com/post/77211282835/four-numbe...