My takeaways from this:

 * Didn't realize Koum had been working on his idea for 5 years! There are no overnight successes in this business.

* Look, an ACTUAL minimum viable product!!! This is how you do it, kids.

* Vision clearly got bigger and bigger as he went on.

* He had international travel and a global lifestyle in mind from day one.

Embracing non-iPhone and non-Android phones made WhatsApp huge.

They did all the hard work of making their app fast and functional on a thousand different phones.

That's a high degree of difficulty and it's very uh glamorous work.