The single most important top-level trend is the shift to mobile.

Mobile is the perfect example of what is enabling economic growth in the technology sector.

You're going to pull out your phone and try to use whatever is the most appropriate app on your iPhone or your Android device. Yelp saw that very early on. And when we launched the mobile product, we saw immediate growth, and we were stunned.

One of the things we did at PayPal was collaborative filtering and machine learning: looking at patterns of human behavior. We used it there to predict when people would try to cheat the system to get money. But you can predict pretty much any behavior with a certain amount of accuracy.

Media is very different from financial services. People are very fickle and very vocal. They believe that things should be one way and not the other. It's still very rewarding to build products for huge audiences. It feels like you're making an impact.

You can't get married to any one particular plan. That is the biggest lesson I learned at PayPal.