We can send people to the Moon; we can see if there's life on Mars - why can't we get $5 [mosquito] nets to 500 million people?

Sometimes the most important things that we do are things we cannot measure.

On the one hand, I loved being a banker. I loved how numbers could tell a story and how you can invest in ideas and see them translate into products and services and create jobs. What I didn't like, particularly where I was working in Brazil during the debt crisis of the early '80s, was how the poor were excluded from the banking system. I made the decision to try and experiment with whether we could use the tools of banking to extend the benefits of the economy to the poor.

The poor also are willing to make, and do make, smart decisions, if you give them that opportunity.

I feel like I'm a relentless, pragmatic, determined optimist.

When we were walking through the narrow alleys [of the Mathare Valley slums], it was literally impossible not to step in the raw sewage and the garbage alongside the little homes. But at the same time it was also impossible not to see the human vitality, the aspiration and the ambition of the people who live there.

Nothing important happens in life without a cost.