In their 2018 annual letter, Bill and Melinda Gates share the secret to their optimism

Bill and Melinda Gates are presented with the 2016 Presidential Medal Of Freedom by President Obama at White House on November 22, 2016 in Washington, DC.
Leigh Vogel | Getty Images

Last year, Bill and Melinda Gates celebrated their close friend Warren Buffett's optimism in their foundation's annual letter. In their 10th annual letter released Tuesday, the billionaire couple revealed the secret to how they stay optimistic.

"Being an optimist isn't about knowing that life used to be worse. It's about knowing how life can get better. And that's what really fuels our optimism," they wrote.

Called the "The 10 toughest questions we get," the letter starts by pointing out that "optimism seems to be in short supply" these days.

"The headlines are filled with awful news," they wrote. "Every day brings a different story of political division, violence or natural disaster."

Nonetheless, the couple says they "see a world that's getting better."

Through the Bill and Melinda Gates Foundation's research and initiatives to help countries facing challenges in education, poverty, hunger and health, the couple has worked at advancing equality around the world.

"Although we see a lot of disease and poverty in our work — and many other big problems that need to be solved — we also see the best of humanity," they wrote.

In a roughly two-minute-long video titled "The evidence for optimism," Melinda Gates reviewed data that showed how the world saw a drop in child mortality from 11 million deaths to five million deaths in the course of 16 years.

"To know that the world, in that span of time from 1990 to 2016, can cut childhood deaths in half makes me incredibly optimistic that we will cut that number in half yet again," she said.

They also attributed their optimism to "learning from scientists who are inventing cutting-edge tools to cure disease," speaking with government leaders around the world who "are being creative about prioritizing the health and well-being of people" and meeting people "who are imagining new ways to transform their communities."

Through the rest of the letter, Bill and Melinda further detail their optimism for global change by answering the following 10 "tough questions" they often get asked:

1. Why don't you give more in the United States?
2. What do you have to show for the billions you've spent on U.S. education?
3. Why don't you give money to fight climate change?
4. Are you imposing your values on other cultures?
5. Does saving kids' lives lead to overpopulation?
6. How are president Trump's policies affecting your foundation's work?
7. Why do you work with corporations?
8. Is it fair that you have so much influence?
9. What happens when the two of you disagree?
10. Why are you really giving your money away — what's in it for you?

In the foundation's 2017 annual letter addressed to Warren Buffett, Melinda Gates wrote that she believes "optimism is a huge asset."

"We can always use more of it. But optimism isn't a belief that things will automatically get better; it's a conviction that we can make things better," she wrote.

It's this very attribute that the billionaires say they admire about Buffett and apply in their personal and professional lives.

"We're trying to channel your empathy, add your optimism, mix in technology, apply strategy, and work with partners to save more lives," Melinda Gates wrote.

They hope people will "be just as optimistic as we are" after reading the responses to their 10 tough questions.

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