You can be happy starting today! Don’t sit by any longer, while friends and co-workers enjoy the good life. Happiness is yours for the taking: All you have to do is reach out and grab it.

So goes the message of countless self-help books and motivational videos, and the mantra of many a life coach. It’s been the thesis of a long and growing list of magazine stories and newspaper articles. It’s the appeal of a good number of serious psychology books, based on scientific research.

The last decade has been a golden era in the rigorous study of happiness, with researchers defining, ever more precisely, what makes us happy. And while the scholarship is new, it builds on a long national tradition of articulating happiness as one of life’s fundamental goals. The pursuit of happiness has been right up there with life and liberty since the country’s foundation.

Now, though, there is gathering evidence that happiness is not what it may appear. A string of new studies suggests that the modern chase after happiness – and even happiness itself – can hurt us. Happy, it turns out, is not always the way you want to be. To be happy is to be more gullible. Happy people tend to think less concretely and systematically; they are less persuasive. A happy person is less likely to discern looming threats.

And the chase itself can backfire: The more you value happiness, it turns out, the more unhappy you will become. The problem, a team of psychologists reports, is that when you focus too much on happiness, you are disappointed when happy events – your birthday party, say – don’t deliver a bigger boost. Which makes you unhappy. Reach for happiness with both hands, and it will abandon you.

“We have put happiness under the microscope just like we do with every other mental state,” says June Gruber, an assistant professor of psychology at Yale University, who coauthored a recent review of happiness research, “and we see that there is this dark side.”

Gruber and her colleagues are not exactly arguing that we should be perpetually bummed out. Happiness still boasts a long list of advantages, beyond the obvious: Positive emotions bring expansive thinking, and promote the bonds that hold society together. Happy people are more flexible thinkers and observers, and this can bring creative insights. Happiness promotes physical and mental health.

The public, though, tends to think of happiness as an unalloyed good. Some have even suggested measuring the progress of nations by the advancing happiness of its citizens. But, Gruber and others suggest, there’s a more accurate way to think of happiness. Happiness is beneficial in some contexts, a hindrance in others; good in moderation, but a poison in excess. It is better to think of happiness, like any emotion, as a set of trade-offs – and a foolish goal to pursue without an understanding of its dark side.

Is there an ideal level of happiness? That’s a philosophical question, to be sure – but one that psychologists have taken a shot at. In 2007, the University of Virginia’s Shigehiro Oishi and two colleagues examined the upper reaches of happiness, with an eye toward different areas of human endeavor. The highest levels of happiness, they found, predicted the most success in close relationships. Very happy people, they suggest, are more likely to idealize their partners, and less likely to walk over to that piece of eye candy at the end of the bar.

However, in two other areas – income and education – peak success comes when happiness is dialed back a bit. For example, they cite a study which looked at the “cheerfulness” of incoming college freshmen in 1976, and compared it to their salaries in 1995. The lowest average incomes were reported by those in the bottom 10 percent of the happiness scale: $54,318. Those in the top 10 percent reported income of $62,681, but the highest earnings, $66,144, came to those who were merely “above average” in happiness. The pattern is the same in income studies of British and German workers. Likewise, a study of University of Illinois students found the highest GPAs not among those who were the happiest, but among those who were merely pretty happy.

The reason, it seems, is that the promise of more happiness is a carrot that spurs us to action. If we are already sated – if we’ve already achieved happiness itself – then why strive? This interpretation fits neatly with a recent study in the Journal of Experimental Social Psychology which found that positive fantasies about future achievement actually increase the odds of failure. Close your eyes and visualize that bright future for yourself . . . and part of you just doesn’t want to work as hard.

Success, of course, lies in the eye of the beholder. What does income matter, some might say, or even learning more in school, if one could give that up and be happier?

But even if you believe that, you have to understand that you will pay a price. Psychologists have documented a set of cognitive deficits, dangerous in some contexts, that come with the warm wash of feeling that all is right with the world. In situations that demand careful attention to novel information, happy people do not perform as well. When you are a little bit sad, you are more ready for trouble, scanning around you for signs that something has gone awry. When you are happy, you are more oblivious.

“You don’t want to be too happy if you are monitoring a nuclear power plant,” says Sonja Lyubomirsky, a professor of psychology at the University of California Riverside and author of “The How of Happiness.”

It is increasingly clear that emotions shape our thinking style, and that this accounts for many of the errors a happy mind makes, according to Joe Forgas, a professor of psychology at the University of New South Wales in Sydney who has devoted considerable energy to documenting the power of negative thinking. When Forgas compares the performance of happy people with those who are slightly sad, he finds that happy people are less reliable eyewitnesses, less able to detect when they are being lied to, and less effective at persuading someone. Happy people are more prone to stereotypes as well.

All of this suggests that the big-picture, positive thinking that comes with happiness brings with it a necessary weakness: a lack of attention to detail, a downplaying of potential threats and problems.

One well-known study of bright children revealed this trade-off in a somewhat macabre fashion. The children, who were followed starting in the 1920s, were assessed for their “cheerfulness,” among other things. The most cheerful kids, it turned out, were also quicker to end up dead. The reasons are unclear – more recent studies generally suggest happier people live longer – but one possibility is that the happiest people don’t do things they should (buckle a seat belt, take a doctor’s advice) because they figure they’ll be fine.

But what of the happiness hedonists – the men and women who, downsides be damned, just want to feel good? For them, the most alarming news is likely to be the way that happiness responds to the chase. The University of Denver’s Iris Mauss set out to understand the relationship between how much people value happiness, and how happy they are. One would expect, of course, that people who valued happiness would indeed be happier, the way valuing baseball cards would lead to a large collection.

Instead, Mauss and her team found the opposite. For example, they showed a euphoric, moving film clip of the skater Sarah Hughes winning a gold medal, the tears of joy, the elation of family and fans. Those who valued happiness more ended up less happy than the rest after viewing the clip. In another, survey-based study, Mauss found that people who valued happiness more tended to be less happy than others when times were good.

When people value happiness, they strive to achieve it, Mauss explains, but that also becomes the standard by which they judge themselves. The disappointment is toxic.

There is a second pernicious force at work: Those who seek happiness tend to be more focused on themselves. (How happy am I? How do I do better?) As these people loosen their social connections, Mauss has shown, they tend to feel more lonely – a direct path to unhappiness. Mauss is a psychologist, running carefully controlled experiments, but her conclusions hint at a broader problem with American culture.

What is to be done? It is not so unreasonable to want to be happier. Are we really just supposed to stand by and let life have its way with us?

Well, yes and no. One of the most powerful ways to boost happiness, ironically, is to learn acceptance. Instead of viewing negative emotions as a failure, learn to see them as a healthy, natural part of the human drama. Negative feelings are often there to tell us something, an invitation to reflect, to make a new plan, or examine an issue more slowly and carefully. This basic notion can play an important role not just in therapy, but also in a balanced, meaningful life.

“The one-sided cult of happiness is neither realistic nor helpful,” Forgas told me in an e-mail. “I think we all need to accept that our lives contain both happiness and sadness, and we should learn to accept and deal with the whole range of human emotions.”

The happiness backlash might also be sidestepped, paradoxically, by avoiding an excessive focus on oneself, or on happiness. So, for example, you might think about what you can do to build stronger relationships with friends and family. You could do things that will bring joy to friends, family, or perfect strangers. These things, the psychological literature suggests, will bring you dividends in well-being. But, hopefully, you will come to see that that is not really the point.

There is admittedly something distinctly un-American about this position: acknowledging not just that perfect happiness is not always a worthy goal, but that some goals cannot be attained directly. Our culture has a strong vein of the can-do: Set out your goals, doggedly pursue them, and you will get there eventually.

However, well before the modern study of happiness, that very American thinker Henry David Thoreau understood the matter perfectly: “Happiness is like a butterfly: the more you chase it, the more it will elude you, but if you turn your attention to other things, it will come and sit softly on your shoulder.”

Or, expressed in the blunter language of a life coach: Happiness can be yours. Just don’t try to grab it.