Sometimes being a social scientist comes in handy. Or at least it did for Arthur Brooks.

He wanted to explore why some people were happy in the second half of life and how he could make sure he — and others — could enjoy those decades.

Aging can be hardest for strivers, Brooks said, who sometimes mourn that their biggest successes are in the rearview mirror.

He advises those still in the first half of their working life to take the long view now and for everyone to build in flexibility and be ready to adjust their expectations.

Brooks' new book is From Strength to Strength: Finding Success, Happiness, and Deep Purpose in the Second Half of Life. He spoke to All Things Considered about not leaving happiness to chance and about the two types of intelligence needed for happiness.

This interview has been edited for length and clarity.

On cracking the code to happiness in the second half of life

You've got to do the work. You can't just wish for it, and you can't hope you get lucky.

The point of the work that I'm doing as a social scientist is to not leave your happiness up to chance but to remarkably increase the odds by doing the work at 25 and 45 and 65 so that by the time you're 75 and 85 and beyond, you're happier than you've ever been.

And I found that there are people who have cracked the code but, more importantly, that we don't have to leave happiness in the second half of life up to chance. We can find a new kind of success if we're willing to make some jumps and some changes and show some humility and have an adventure that's better than the first half.

On the intelligence needed for happiness

There's a very interesting set of findings that said success early on is based on one of two types of intelligence. The first is called fluid intelligence, which gives you the ability to solve problems, to crack the case, to innovate faster and to focus harder than pretty much all the competition early on in your career. This is your Elon Musk brain, and this increases through your 20s and into your 30s.

But then it tends to decline through your 40s and 50s, meaning that you need to move to the second kind of intelligence, which is increasing in your 40s and 50s and even your 60s, and it will stay high for the rest of your life. That's called your crystallized intelligence, which is your wisdom, your ability to compile the information that's in your vast library to teach better, to explain better, to form teams better. In other words, not to answer somebody else's questions, but to form the right questions.

On staying flexible

One of the biggest things that I teach my students at the Harvard Business School is that what you think right now is not what you're going to think later. The things that you want are not the things that you're going to want later.

Your abilities are going to change. Your views are going to change. The things you care about [are] going to change, and that's good and that's healthy. And that kind of flexibility is key.

On using the pandemic's pause button

Everybody knows that the pandemic is not something that we wanted, but it's also been an incredible opportunity for a lot of people. For me, I was able to quietly write this book and set up a strategic plan for the rest of my life.

A lot of other people tell me similar stories and how they deepened their relationships — that they understood themselves better. And this is something that we should remember as we get back into the hustle and bustle of non-pandemic life.

Let's not forget that there are certain things that we don't want to go back to.

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