In the developing world, they don't have smartphones yet. They have the older plastic phones, but women are saving money on those, because they don't have access to banks. Having that access to digital money changes everything for her because she actually doesn't have to negotiate with her husband, which she will tell you is very hard in these circumstances, especially when the means are meager. She's expected to have money to pay for the kids' health or to help with the school fees.

I went to business school, and I went straight from that to a nine-year career at Microsoft. Eventually, I ran a big chunk of the consumer products division for Microsoft.Then I left with the birth of our first daughter because Bill and I both wanted to have a few kids.

If you don't invest in the woman, empower her, give her the things she needs to lift her family up, you're just not going to make the progress that you want to make. But if you put her at the centre, you can change a lot for that family, and it has ripple effects through the economy.

You can't save kids just with vaccines.

Any social or cultural change has to be made openly and with people agreeing. You don't get there by just pushing an outsider's point of view.

What great changes have not been ambitious?

I've travelled extensively in the last 16 years - to slums in Bangladesh, to townships in South Africa, to all kinds of places in India, etc. When I would go and talk to villagers about something like vaccines, if I stayed long enough, the women would bring the conversation around and say: "What about this family planning tool? We can't keep having the number of children we're having."