If you're using first-class land for biofuels, then you're competing with the growing of food. And so you're actually spiking food prices by moving energy production into agriculture.

As you get to the end of the project you want to run all the tests cases against one version and make sure that you know that that version passed everything. And so as you get late in the project you get a little more conservative about making radical changes to the software.

Take agriculture, where we haven't done much, or sanitation; saying, "okay, we will be able to make a really huge effort there." It really energized the foundation and half of what we've gotten done in this last decade is because Warren [Buffett] trusted us.

Corruption is one of the most common reasons I hear in views that criticize aid.

With polio, we've gone several years with no polio in all of Africa, but now with this we're having to go and mop up in that whole region, so it's a bit of a setback for polio. So in parallel we have to go back and get rid of those cases.

When you have a product that has zero sales, it is easy for people to say whatever they want about it and almost fantasize about it.

You can make money and you can make excuses, but you can never make money out of excuses