Melinda Gates isn’t the kind of billionaire philanthropist who simply signs off on a donation. The former Microsoft General Manager puts boots on the ground in the communities she seeks to help. She comes face-to-face with the people who benefit from the medical care she and her husband, Bill Gates, fund via The Bill and Melinda Gates Foundation – the largest private charity in the world.

People like Meena, a woman who gave birth at one of their health clinics in India’s north in 2010. Speaking to Oprah’s Super Soul Sunday last month, Melinda recalled how she asked this young mother a simple question: ‘Do you want to have more children?’

“Eventually, after a very long pause, she looked up at me and she said, ‘I can’t have anymore children… I don’t have any hope for these two children. I have no hope. I can’t hardly feed these kids. My only hope is if you take my two boys home with you.’

“I had to beg her for her forgiveness, and I just said, ‘I just can’t. I am sorry, but I can’t. I have three children of my own at home. I know you love these boys. [But] I can’t.’ It was crushing.”

It was the first time a loving, desperate mother asked Melinda to take her children. But it wasn’t the last.

It’s encounters like this that capture the unique moral dilemma of the uber-rich. Who do you help? Where? And how much?

Speaking to Melinda Gates, fellow billionaire Oprah Winfrey noted the weight of the responsibility that comes with being in a position to affect meaningful change. Though she's donated hundreds of millions to charity, including more than US$140 million alone to maintain her Leadership Academy for Girls in South Africa, she revealed that she struggles not to be affected by the calls that can't be answered.

"You don't want to have to take it all in, because - like a lot of people - you feel like, 'If I take it in, then I'm going to have to do something, and what can I do when I'm already helping people over here?'" she said.

As one of the world's most high-profile billionaires (net worth US$2.9 billion) and a famously generous philanthropist, people have gone to extraordinary lengths to draw Oprah's attention to their causes. An animal shelter once purchased a billboard near the offices of her Chicago production company, Harpo, to alert her to the inhumane practises of mass-breeding puppy mills - 'The dogs need you', it read. "That actually worked,” Oprah told Forbes. An entire show was dedicated to the cause.

"I really considered giving it all away."

Abigail Disney, the granddaughter of Walt Disney, is one of the heirs to her family's immense fortune.

Over the past 30 years, she's donated more than US$70 million to causes including her own charities that focus on poverty and female leadership in peace-building. And she's in a position to keep giving for the rest of her life. But it's something she struggled with.

"I really considered giving it all away at a certain point in my 20s, and I know people who did that," Disney told The Cut in March. "And I wish I could tell you that it was courage that kept me from doing that, but it was mortal fear. I didn’t think I would be able to survive.

"Now I’m glad I didn’t give it all away, because my money has grown. Now I’ve given away so much more than I inherited. And I’m so much smarter now. What I would’ve done in my 20s would have been great and nice, but I’m so much more effective now."

Effectiveness is at the root of the dilemma. While on paper, Melinda Gates certainly has the means to take in another woman's child, for example (she's worth an estimated $70 billion) she knows her impact can be far broader.

Often, she told Oprah, she'll liaise with local organisations to ensure individuals like Meena are directly supported. But it's about finding a more effective solution.

"We have to lift up everybody," she said. "Meena's story, that she had the courage to share with me, is the story of hundreds of millions of women. These resources that Bill and I have, we have to put them to lift up hundreds of millions of men, women and children; not just the one."

Ultimately, the "heartbreaking" encounter with Meena, and other mothers like her, led Melinda Gates to recognise the life changing - and life-saving - potential of contraceptives for women in low socioeconomic regions. It compelled her to raise $2.6 billion and launch a global coalition on family planning.

As she writes in her book, The Moment of Lift, "The starting point for human improvement is empathy. Everything flows from that."