Part 1 of the Netflix documentary series Inside Bill’s Brain tells the story of the Gates Foundation’s quest to rethink sanitation for the world’s poorest. First step: reinvent the toilet! This belief in the power of innovation has been a constant in my life, starting from the time I fell in love with software in high school to my work today at our foundation. What follows is the story of a moment of clarity for me on that path and the influence of someone who’s been a critical guide along the way.

If you’d have asked me in my twenties if I’d ever retire early from Microsoft, I’d have told you that you were crazy. I loved the magic of software, and the ever-rising learning curve that Microsoft provided. It was hard for me to imagine anything else I’d rather do.

By my mid-forties my perspective was changing. The U.S. government’s antitrust suit against Microsoft had drained me, sucking some of the joy out of my work. Stepping down as CEO in early 2000, I hoped to focus more on building software products, always the best part of my job.

Also, my world view was broadening. Both Melinda and I were feeling a strengthening pull toward our young foundation and its work in U.S. education and the development of drugs and vaccines for diseases in poor countries. For the first time in my adult life I allowed myself space for non-Microsoft reading, soaking up books on the immune system, malaria and the history of plagues just as I had once scoured The Art of Computer Programming.

With our commitment to philanthropy growing, Melinda and I transferred $20 billion of Microsoft stock to our foundation, making it the largest of its kind in the world. Within a year I’d taken my first overseas trip for the foundation, to India, where I squeezed drops of polio vaccine into babies’ mouths. Melinda traveled to Thailand and India to study how those countries were handling AIDS.

Our good friend Warren Buffett was curious about this new journey we were on. So in the fall of 2001, he invited me to a resort in West Virginia and asked me to speak to a group of business leaders about what Melinda and I were learning.

I’m not a natural public speaker. But at Microsoft, speech after speech, year after year, I learned to step out on a stage and paint a vision of technology for our customers, partners and the media. It helped that people wanted to hear about the white-hot software industry. I grew to enjoy it.

I felt like I was starting over with our foundation. At big global meetings, like the World Economic Forum, people flocked to hear me detail some cool piece of software, but the crowd and the energy would be gone when later that day I’d announce an innovative plan to get vaccines to millions of children.

At the time, many people I met thought health problems in low-income countries were so big and intractable that no amount of money could make any significant difference. I could see why. It was easy to ignore death and disease happening so far away. And so much of what we read in the news about global health focused on doom and gloom. This frustrated me. The problems were real enough, but so is the power of human ingenuity to find solutions. Melinda and I felt a strong sense of optimism, but we didn’t see that reflected in these stories.

Right around the time Warren asked me to give the talk, Melinda and I were trying to figure out how we might use our voices to raise the visibility of global health. Would anyone listen?

My speech to Warren’s friends was a chance to practice. If I could stir them, it would be a step towards persuading the people with the power to make the biggest difference: the legislators and heads of countries who decide how much money flows into foreign aid and global health.

I was a little nervous heading to the conference room where Warren’s group was gathered—but more than that, I was exhausted. We were in the midst of negotiations over the antitrust case, and I’d been on the phone with lawyers deep into the night. I hadn’t had time to write a full speech. I’d just jotted notes between calls, trying to simplify all we had learned into the clearest possible story.

I started talking, haltingly at first. Our big revelation, I explained, had come in the mid-1990s when Melinda and I realized how much misery in poor countries is caused by health problems that the rich world had stopped trying to solve because we’re no longer affected by them. That incensed us. The cost of that inequity at the time was three million children dying ever year, I said.

Those deaths, we realized, weren’t caused by a bunch of runaway diseases, but by a handful of illnesses that are largely treatable. Diarrhea and pneumonia alone were responsible for half of the deaths among children. Many of those children could be saved with medicines and vaccines that already existed. All that was lacking were incentives and systems to get those life-saving technologies to the people and places where they were needed—and some new inventions to speed the change.

Our philanthropy, I explained, followed the same philosophy that guided Microsoft: relentless innovation. The right vaccine can wipe a deadly virus off the planet. A better toilet can help stop diarrheal disease. Investments in science and technology can help millions to survive their childhood and lead healthy productive lives—potentially the greatest return in R&D spending ever.

As I spoke, the legal tangles that had consumed me the night before vanished. I was energized. When ideas excite me, I rock, I sway, I pace—my body turns into a metronome for my brain. For the first time, all the facts and figures, anecdotes and analyses cohered into a story that was uplifting—even for me. I was able to make clear the logic of our giving and why I was so optimistic that a combination of money, technology, scientific breakthroughs, and political will could make a more equitable world faster than a lot of people thought.

I could tell from the nods and laughs and caliber of questions that the group got it. Afterward, Warren came over with a big smile. “That was amazing, Bill,” he said. “What you said was amazing, and your energy around this work is amazing.” I grinned back at him. Three ‘amazings’—a first.

The confidence I found that day encouraged me to take a more public role on global health issues. Over the next year, I refined my message at events and in interviews. I spent more time talking about health with government leaders. (That’s now a big part of my job.)

But something else had happened, too. The speech helped me see more clearly a life for myself after Microsoft, centered on the work that Melinda and I had started. Software would remain my focus for years and I will always consider it the thing that most shaped who I am. But I felt energized to get further along this new path we were traveling, to learn more and to apply myself to the obstacles in the way of more people living better lives. Eventually, I would retire from Microsoft almost a decade earlier that I had planned. The 2001 speech was a step, a private moment, on the way to that decision.

Now I get to focus every day on trying to deliver the vision I outlined in that conference room almost two decades ago. The world is more equitable now than it was then. But we’ve still got a long way to go. By letting Netflix’s cameras in, I hope you can see the joy I get from my work and why I am so optimistic that with ingenuity, imagination, and determination, we can make even more progress towards that goal.