The main motivations were to try to leverage Google's expertise with large computer systems and to try to give something back to science

Things are always changing. Part of being successful here is being comfortable with not knowing what's going to happen.

There are unlimited opportunities for display advertising. In fact, we're in the process of massive change in the display industry - how it's bought, how it's sold, and how it's targeted.

We are a consumer company and our success is directly linked to our users trusting us. Therefore we have the same incentive as the user: they want to see relevant advertising so their experience of Google is positive and we want to deliver it.

Right now, offline and online are coming together because of smartphones.

Rarely are opportunities presented to you in a perfect way. In a nice little box with a yellow bow on top. 'Here, open it, it's perfect. You'll love it.' Opportunities -- the good ones -- are messy, confusing and hard to recognize. They're risky. They challenge you.

I have had a lot of setbacks that I have learned from.