Our actions - and inaction - touch people every day, people we may never know and never meet.

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.

So many low income people have seen so many failed promises broken and seen so many quacks and sporadic medicines offered to them that building trust takes a lot of time, takes a lot of patience.

People have to understand that unless social enterprise is experimental, it will not succeed in making a difference.

Entrepreneurs are the seekers of solutions, and that they will go into these places where both market and traditional aid has failed or traditional charity has failed.

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?

Four billion people on Earth make less than four dollars a day.