Maybe you are aware of Facebook's WhatsApp acquisition. If you didn't know till now then maybe you are away from internet because internet is flooded with this. Acquisition of WhatsApp by Facebook is really most expensive. Here's a chart by statista showing acquisition of some other companies and this one is on the top of them.
I hope you already know that Instagram was also acquired by Facebook but only for $1 billion. Now, like me, you'll think why Facebook paid that much to acquire WhatsApp. What is in it which made Facebook to give them $19 billion?