I would say the discovery of the hydrothermal vents off the Galápagos Islands. That really turned science upside down. Until that time, there were a lot of things we didn’t know about the ocean. We didn’t know why it was salty. We didn’t know why it had the chemistry that it had.

One does have to point to the fact that we did achieve an agreement, that we had that agreement endorsed by a majority of the people of Northern Ireland; that despite very considerable political difficulties since then, we have actually managed to implement the greater part of the political agenda of that agreement, and we have restored local parliamentary institutions in Northern Ireland, that we have a local administration in place which is working, maybe not working ideally, but is still actually there. Those are the significant political developments that one’s had a hand in and obviously, one would point to that as being the things that one looks back at with most satisfaction, but I realize that it’s still work in progress.

And then in 1974 I started to work on phosphorous chemistry which is the area of which I’m most proud as it turns out. I’m most proud of my work on carbon phosphorous chemistry.

I’m the most proud when I get something from cities, or people. At first I was against awards, you know. I would always say, “This is so fake. The people who vote on this stuff, they never listen to the music.” But for me it’s when I received awards or something from the city. Just to go to somebody’s house and eat. Or people come and say, “We spent our anniversary checking you out,” or “We were making love to one of your records, and we had a child!” See that kind of stuff makes me feel good. Like you get a key to the city and the people are really into it. Not just, “Oh, let’s give him the key to the city because he got some publicity.” It will be some people you knew, and you were there at their school, and you worked in the community.

If you ask me where has been the one area where I feel that I've been most frustrated and most stymied it is the fact that the United States of America is the one advanced nation on earth in which we do not have sufficient common-sense, gun-safety laws. Even in the face of repeated mass killings. … And for us not to be able to resolve that issue has been something that is distressing. But it is not something that I intend to stop working on in the remaining 18 months.

One of the things that Michelle and I are proud of is that we came through the White House with our souls intact. Everybody has heard: Power corrupts. I do think if you are placed in such an artificial situation, and your office has great importance, there is a tendency for people to want to please you. To not be as honest with you. We fought against that.

I would end every night reading these ten letters. It made the numbers and the policies very concrete and very specific. And I was reminded that the choices we were making were affecting millions of people. I found that to be very useful.

People ask me sometimes, who inspires you, Mr. President? Those quiet heroes all across this country -- some of your parents and grandparents who are sitting here -- no fanfare, no articles written about them, they just persevere. They just do their jobs. They meet their responsibilities. They don't quit. I'm only here because of them. They may not have set out to change the world, but in small, important ways, they did. They certainly changed mine.

You'll see I wear only gray or blue suits. … I'm trying to pare down decisions. I don't want to make decisions about what I'm eating or wearing. Because I have too many other decisions to make. … You need to focus your decision-making energy. You need to routinize yourself. You can't be going through the day distracted by trivia.

The thing actually that I most dislike is cruelty. I can't stand cruel people. And if I see people doing something mean to somebody else, just to make themselves feel important it really gets me mad.