On this day: Facebook's IPO and the moment ad-tech got repriced

On May 18, 2012, Facebook went public at $38 per share, valuing the company at $104 billion. The stock dropped under $20 within three months. Analysts wrote obituaries. A year later the stock was up, the mobile ad business was growing 100%, and the company was on its way to being the largest ad platform in history.

The lesson that stuck: mobile ad revenue, which barely existed as a category at IPO, became 80% of Facebook's revenue inside 18 months. The pivot happened quietly, mostly in engineering, while the finance community was writing the eulogy.

The hardest judgment in investing and operating is separating "permanently broken" from "temporarily repricing." Facebook looked like the first. It was the second. Most businesses going through public pain fall somewhere between. The operators who've lived through one cycle know how to tell which is which.