The authors are co-chairs of the Bill & Melinda Gates Foundation. Their 2018 annual letter, from which some points in this article are adapted, is available at www.gatesletter.com. The opinions expressed in this commentary are theirs.

(CNN) "Is it fair that you have so much influence?"

We've been asked that question more than a few times in the 18 years since we started our foundation. Our answer? No. It's not fair that we have so much wealth when billions of others have so little. And it's not fair that our wealth opens doors that are closed to most people.

However, we do this work, and use whatever influence we have, to help as many people as possible and to advance equity around the world.

Bill Gates

Melinda Gates

And we are committed to being open about what we fund and what the results have been. (It's not always clear what's been successful and what hasn't, but our foundation team works hard to assess our impact, course correct and share lessons.) Although we've had some success in getting the world to pay more attention to health and extreme poverty, it would be hard to argue at this point that we made the world focus too much on them.

Having influence does make it harder to get honest feedback, though. In business, your customers will tell you in an instant when you've made a mistake. It's not the same in philanthropy. Some of our critics don't speak up because they don't want to risk losing their funding from us. That's why hearing and answering tough questions is important. And it means we need to hire well, consult experts, learn constantly and seek out different viewpoints.

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