The lives of the world's poorest people have improved more rapidly in the past 15 years than ever before, and I am optimistic that we will do even better in the next 15 years. After all, human knowledge is increasing.
OPINION: We can see this concretely in the development and declining costs of new medicines like HIV drugs and in the creation of new seeds that allow poor farmers to be more productive.
Once such tools are invented, they are never un-invented. They just improve.
Sceptics point out that we have a hard time delivering new tools to the people who need them.
This is where innovation in the measurement of governmental and philanthropic performance is making a big difference.
That process - setting clear goals, picking the right approach and then measuring results to get feedback and refine the approach continually - helps us to deliver tools and services to everybody who will benefit.
Innovation to reduce the delivery bottleneck is critical.
Following the path of the steam engine long ago, progress is not "doomed to be rare and erratic". We can make it commonplace.
Although I am an optimist, I am not blind to the problems we face or to the challenges we must overcome to accelerate progress in the next 15 years.
The two that worry me the most are that we will be unable to raise the funds needed to pay for health and development projects, and that we will fail to align around clear goals to help the poorest.
The good news is that many developing countries have growing economies that allow them to devote more resources to helping their poorest people.
India, for example, is becoming less dependent on aid and eventually will not need it.
Some countries, such as the United Kingdom, Norway, Sweden, South Korea and Australia, are increasing their foreign-aid budgets. Others, even traditionally generous donors such as Japan and the Netherlands, have reduced theirs.
The direction of many countries, including the United States, France, Germany and Canada, is unclear.
Still, aid is critical. It helps people in the poorest countries to meet their basic needs. It funds innovation in the creation of new tools and services, and in their delivery.
Unfortunately, aid budgets are threatened by fiscal weakness in almost all of the advanced countries. Unless voters hear about the positive impact that their generosity is having, they will inevitably focus on issues closer to home.
A single story, true or not, about a small amount of aid being misused can often cloud the entire field. Imagine how you would feel about investing if every article you read were only about stocks that did poorly, with no reporting on the big successes.
Historically, aid was discussed largely in terms of the total amount of money invested, but now that we are measuring indicators like child mortality more precisely, people are able to see the impact that aid has in stark terms. That it means the difference between, say, giving people access to HIV treatment and letting them die. When framed this way, aid has a better chance of becoming a priority.
But will the world align around a clear set of goals in the next 15 years? The United Nations is starting to map out new goals for the years following the 2015 expiration of the current Millennium Development Goals.
As with the MDGs, the next set of goals could help to align groups doing the work, remind voters what their generosity supports and allow us to see where we are making progress in delivering solutions to the poor.
The MDGs' success means that there is a lot of interest in expanding them to include a broader set of issues. But many of the potential new goals lack unanimous support, and adding a lot of new goals - or goals that are not easily measurable - may sap momentum.
The MDGs were coherent because they focused on helping the poorest people in the world. The groups that needed to work together to attain them were easy to identify and they could be held accountable for co-operation and progress. When the UN reaches agreement on other important goals, such as mitigating climate change, it should consider whether a different set of actors and a separate process might be best for those efforts.
The progress that the world has made in helping the poorest in the past 15 years is the kind of good-news story that happens one life at a time, so it often does not have the same visibility as a big setback.
From time to time, we should step back and celebrate the achievements that come with having the right goals, the necessary political will, generous aid and innovation in tools and their delivery. Doing so has certainly deepened my commitment to this work.
* Microsoft founder Bill Gates is co-chairperson of the Bill & Melinda Gates Foundation.
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