In the spring of 2012, around the time that Facebook purchased Instagram for roughly $1 billion, I was teaching an M&A class.

At the time, I had difficulty explaining why Facebook would pay that amount of money for a company that was not only not profitable, but also had no revenue. I spoke as someone trained to use multiples EBITDA and as someone who did not (and still does not) have an Instagram account.

Now, over four years later, Forbes estimates Instagram's value at $25billion to $50billion. That valuation still requires some creativity, as Instagram had sales of "only" $630 million in 2015. Instagram, however, has added roughly 100 million new users in the last 9 months and is projected to have revenue of $1.5billion this year. While there is reason to be wary of projections, the projected sales for Instagram in 2018 is an impressive $5billion.

This drives home that valuation is as much art as science, and the conventional valuation methods will not work well for every company. In that deal, I imagine Instagram's technology, brand, and the user base were all large value drivers. With the benefit of hindsight, Instagram is looking like a good acquisition for Facebook, even if the current projections end up being a bit optimistic.