Many of us worry about what our lives will be like in our final years. But after spending a year following six people ages 85 and older, The New York Times reporter John Leland came to some surprising conclusions about old age and contentment later in life. His work inspired his book, Happiness Is a Choice You Make: Lessons From a Year Among the Oldest Old (Sarah Crichton Books, $16), which comes out in paperback in January. In this lightly edited conversation with Associate Editor Mary Kane, Leland talks about applying the wisdom of the oldest old to our lives at any age.

You write, “If you want to be happy, think like an older person.” Can you explain how that works?

We know from a lot of research that older people are more content with their lives than younger people are. Thinking like an older person is thinking about resilience and focusing on what is as opposed to what is not. Accepting your mortality by not being so afraid of it. When you are older, you view the time horizons in front of you differently. You understand the days are finite, and we might as well enjoy the ones we have left. The big lesson for me, the really practical one, is waking up in the morning and saying, “Thank God for another day.” It’s the conscious practice of gratitude.

Can you explain what you call “selective forgetting”?

We do forget the horrible things in our lives to a great extent but not entirely. The traumas of our lives stay with us. But we’re constantly writing the stories of our lives, and there are lots of things we’re filtering out. Usually our stories are about the positive things. That flu that almost killed you—you forget about how miserable you were. You just remember that it didn’t kill you. That friend you made when you were 14—that’s something you remember.

[The people I interviewed] saw loss as part of what it is to be human. It doesn’t make loss any more fun. But you’re not being singled out for punishment. You’re sharing that same experience with every other person that’s ever lived.

What do you mean when you say happiness is a choice?

You come to understand that the quality of our lives isn’t based in the events of our lives. It’s really in the reaction to the events in our lives. That’s a really useful thing, to realize “I don’t have control over some of the events in my life, like the weather, but I actively have a say in how I respond to the weather.” The title of the book is Happiness Is a Choice You Make, but the key word isn’t happiness. It’s choice. It’s declaring that you won’t be defined or determined by the circumstances of your life. You have a say in this. That declaration is liberating. That liberation is happiness. Happiness isn’t just the thing you choose; it’s the act of choosing it that makes you happy.

You talk about the essence of what you learned: “to shut down the noise and fears and desires that buffet our days and think about how amazing, really amazing, life is.” Can we all do this?

There are things we can do to change our ways of thinking and improve the quality of our lives. I’m not talking about depression, which is a serious illness that kills people and needs to be treated. But you can be focusing on what is, not what you don’t have and what you’re missing. Optimism doesn’t mean the future is going to necessarily be better. It means seeing that the present is better.

We are so detached from the oldest old, in a way previous generations were not. How can we address that?

We think of old age as some sort of place to visit—and not a pleasant place. But just spending time with the old is sometimes all we can do, and the most important thing we can do. Give older people a chance to talk. Find out what they care about, and what’s important to them. Older people aren’t being asked about what they need. They are being told what they need by people who have never been old.

This article was written with the support of a journalism fellowship from the Gerontological Society of America, Journalists Network on Generations and Silver Century Foundation.