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(CNN) -- People say they know happiness as an emotion, a state of mind and as something to aim for, but when it comes to defining happiness, they are often uncertain how to articulate their feelings.
Experts say people are poor judges at knowing what makes them happy, when they have been happy, or when they will be happy.
Harvard psychology professor Daniel Gilbert explored the broad, often-tongue-tying nature of happiness in his book, "Stumbling on Happiness." He sat down with CNN to discuss the elusive emotion.
CNN: What is happiness?
Gilbert: For me, happiness is substantially just an emotional experience. It's a feeling. It's a feeling that's common to lots of different experiences. When we taste chocolate. When we help a tourist find the art museum. When we see our granddaughter smile for the first time. When we solve a crossword puzzle. These are all very different experiences. But they have something in common. I think that thing they have in common is that feeling we call happiness.
CNN: Do most people know when they're happy?
Gilbert: We know people are very bad at remembering how happy they were. They're very poor at predicting how happy they'll be. They aren't even good at saying how happy they are in general. One thing people can tell you is how happy they are at the moment you ask them that question.
CNN: Why are we so bad at predicting whether we'll be happy in a certain situation?
Gilbert: We're very poor at predicting our future happiness for two sets of reasons. The first is, we have a lot of bad theories about happiness. Our culture and our genes give us disinformation about the sources of happiness. Even if you try to set these aside, it turns out just using our imaginations to project ourselves into the future -- close your eyes and say what would it be like to win a gold medal, to move to Cleveland, to be an architect -- imagination fails us in some very predictable and systematic ways.
CNN: How do culture and genes lead us astray?
Gilbert: You know all human behaviors are the product of two things: Genes and culture. The interplay between these two, genes and culture, are both self-perpetuating systems. They are systems that want to survive, and the way they survive is getting us to do things for them. For example, our genes require that we reproduce. Our culture requires that we consume goods and services. So both our genes and culture conspire to lead us to believe that things like, oh, having children or getting rich will make us very happy. But the data from economics and psychology are abundantly clear. Having children tends to create a small negative effect on people's happiness and having money has a very little relationship to people's happiness, so both of these are bad theories about the kinds of things that will bring us happiness in the future.
CNN: Does money buy happiness?
Gilbert: Anybody who says that money can't buy happiness has never lived in a cardboard box under a bridge. There's a big difference between having no money and having basic needs met. What's surprising about money is once you have a pretty small amount of it, more money stops making you much more happy. So the difference between making $5,000 a year and $50,000 is really quite dramatic in terms of happiness. But the difference between $50,000 and $500,000 isn't nearly as big. That's really a much larger jump, but it creates a much smaller increase in happiness. At some point, you just stop getting more happy from money.
CNN: How about material goods? Can they make us happy?
Gilbert: I think the diminishing returns on money are simply a signal for the diminishing returns on the consumption of material goods. Look, we live in a consumer driven society. We are bombarded every day by messages that tell us the source of happiness is the new stuff. Get more things, and if the old things aren't making you happy it's because you got the wrong things, and you need different things. The truth of the matter is material goods create some form of happiness. Some amount of happiness but not nearly as much as people predict. One mistake that people seem to make is if they invest in durable goods when some studies suggest they'd be happier if they invested money in experiences.
CNN: If you were going to try to improve what will make you happy, how would you go about doing that?
Gilbert: I would abandon imagination entirely. If I wanted to know what a certain future would feel like to me, I would find someone who is already living that future. If I wonder what it's like to become a lawyer or marry a busy executive or eat at a particular restaurant, my best bet is to find people who have actually done these things and see how happy they are. What we know from studies is not only will this increase the accuracy of your prediction, but nobody wants to do it. The reason is, we believe we're unique. We don't believe other people's experiences can tell us all that much about our own. I think this is an illusion of uniqueness. I think people are by and large -- when it comes to happiness at least -- generally the same. The kinds of things that make one person happy are by and large what make other people happy.