As I was having lunch with Jack Sim, he pulled out his phone to show me a countdown app, which revealed he had just over 5,000 days left to live.

When the countdown ends, Jack will be 80 years old – which is about the average lifespan of a male Singaporean.

Jack, the 305th person I’ve met on my quest to have lunch with 500 strangers, told me he feels a sense of urgency to solve big problems before his countdown ends.

Jack is a serial entrepreneur who had a very successful business career. That allowed him to switch from paid work to unpaid philanthropy 26 years ago. As he explained, most people trade time for money, because the latter is more valuable than the former. But once all your material needs are covered, time becomes more valuable than money, at which point the trade no longer makes sense.

When Jack reached that point, he looked around for a big problem to solve. That’s why, on 19 November 2001, Jack founded the World Toilet Organization, which aims to improve toilet and sanitation conditions around the world by promoting market-based solutions and influencing government policy.

Thirteen years later, the United Nations designated 19 November as World Toilet Day.

There’s another big problem Jack is trying to solve. About four billion people live in poverty; by the time he dies, he hopes to have played a part in reducing that number to zero.

Clearly, Jack is a bold thinker. One reason is that he doesn’t have time – both literally and figuratively – for small goals. Another reason, Jack says, is that when you shift your focus from thinking about yourself to serving others, your field of vision grows exponentially.

Jack may do serious work, but he’s got a mischievous sense of humour and delights in asking provocative questions. So I was educated, amused and challenged during our nice lunch.