But the next day I went to Soweto, the poor township southwest of Johannesburg, that had been the center of the anti-apartheid movement.

It was a short distance from the city into the township, but the entry was sudden, jarring and harsh.

I passed into a world completely unlike the one I came from.

My visit to Soweto became an early lesson in how naive I was.

Microsoft was donating computers and software to a community center there.

The kind of thing we did in the United States.

But it became clear to me, very quickly, that this was not the United States.

I had seen statistics on poverty, but I had never really seen poverty.

The people there lived in corrugated tin shacks with no electricity, no water, no toilets.

Most people didn't wear shoes.

They walked barefoot along the streets, except there were no streets, just ruts in the mud.

The community center had no consistent source of power.

So they rigged up an extension cord that ran 200 feet from the center to the diesel generator outside.

Looking at this setup, I knew the minute the reporters left, the generator would get moved to a more urgent task.

And the people who used the community center would go back to worrying about challenges that couldn't be solved by a personal computer.

When I gave my prepared remarks to the press, I said Soweto is a milestone.

There are major decisions ahead about whether technology will leave the developing world behind.

This is to close the gap.

But as I read those words, I knew they weren't super relevant.

What I didn't say was, by the way, we're not focused on the fact that half a million people on this continent are dying every year from malaria.

But we are sure as hell going to bring you computers.

Before I went to Soweto, I thought I understood the world's problems but I was blind to many of the most important ones.

I was so taken aback by what I saw that I had to ask myself, did I still believe that innovation could solve the world's toughest problems?

I promised myself that before I came back to Africa, I would find out more about what keeps people poor.

Over the years, Melinda and I did learn more about the pressing needs of the poor.

On a later trip to South Africa, I paid a visit to a hospital for patients with MDR-TB, multi-drug resistant tuberculosis, a disease with a cure rate of under 50%.

I remember that hospital as a place of despair.

It was a giant open ward, with a sea of patients shuffling around in pajamas, wearing masks.

There was one floor just for children, including some babies lying in bed.

They had a little school for kids who were well enough to learn, but many of the children couldn't make it, and the hospital didn't seem to know whether it was worth it to keep the school open.

I talked to a patient there in her early 30s.

She had been a worker at a TB hospital when she came down with a cough.

She went to a doctor and he told her said she had drug-resistant TB.

She was later diagnosed with AIDS.

She wasn't going to live much longer, but there were plenty of MDR patients waiting to take her bed when she vacated it.

This was hell with a waiting list.

But seeing this hell didn't reduce my optimism.

It channeled it.

I got into the car as I left and I told the doctor we were working with I know MDR-TB is hard to cure, but we must do something for these people.

And, in fact, this year, we are entering phase three with the new TB drug regime for patients who respond, instead of a 50% cure rate after 18 months for $2,000, we get an 80% cure rate after six months for under $100.

(Applause).

Optimism is often dismissed as false hope.

But there is also false hopelessness.

That's the attitude that says we can't defeat poverty and disease.

We absolutely can.