It's a vision problem that no laser surgery can cure, a hyperopia that keeps us from seeing the central source of happiness right next to us. That problem is called adulthood. Those who are afflicted with this condition have trouble focusing on nearby objects of amusement and the realm that delivers the most enjoyment per square inch: play. Adults are oblivious to what they knew as kids -- that play is where you live.

Grownups aren't supposed to play. We have problems. We're too busy. We have important things to do. It turns out, though, that there are few things more important to your happiness than frequent doses of play. As a study led by Princeton researcher Alan Krueger found, of all the things on the planet, we're at our happiest when we're involved in engaging leisure activities. Why not do more of that?

Well, there's the entrenched masochism that we seem to prefer, stemming from the built-in bias against anything that's not full-blast production mode. "Talking about adult play is kind of taboo in our culture," says Lynn Barnett-Morris, of the University of Illinois, Urbana-Champaign, an expert on the effects of play on personality. "We think it's a waste of time or that we could be more productive doing other things -- all sorts of dumb stuff."

We live in a culture obsessed with wringing an external result from everything we do. Play doesn't operate on that metric. It's not about the end but the experience. This has made play one of the last remaining taboos, an irrational deviation from gainful obligation. What we don't realize, though, is that it's precisely the lack of a quantifiable result that allows play to tap a more meaningful place that satisfies core needs and reveals the authentic person behind the masks of job and society.

Anthropologist Gregory Bateson believed that the fixation on making everything productive and rational cuts us off from the world of the spontaneous that is home to real knowledge. Wisdom, Bateson believed, is to be found in the realms outside intentionality, in the inner reaches of art, expression and religion. "The whole culture is suffering from overconscious intentionality, overseriousness, overemphasis on productivity and work," psychologist and cultural explorer Bradford Keeney told me. "We've forgotten that the whole picture requires a dance between leisure and work."

Play isn't a character defect; it's the builder of character, developing persistence, competence, mastery and social skills that take us beyond perceived limitations. It was there in the faces and confidence of stunt-kite fliers, salsa dancers and badminton enthusiasts I met along the road to my new book on the power of participant experience, "Don't Miss Your Life." Everyone I met had dramatically upgraded self-esteem and a sense of self anchored by something that's supposed to be worthless.

Studies show that play reflects more of who you are than your work. When you're engaged in activities of "personal expressiveness," ones that are self-chosen and that reflect intrinsic goals, you're operating from the "true self," says Alan Waterman of the College of New Jersey. This leads to optimal psychological functioning (i.e., happiness). We're talking about something far from tangential to your existence. Play scholar John Neulinger called passionate play pursuits none other than the "central life interest."

Play brings you back to life -- your life. "Adults need to play because so much of our life is utilitarian, the University of South Alabama's Catherine O'Keefe explained to me. "We need to reconnect with the things of our lives that ground us in who we really are and why we like our lives."

When a 40-year-old goes headfirst down a water slide, that person is not 40 anymore. A few decades have been knocked off, because something inside has come alive again. It should be pretty obvious that the animating spark of play is the fast track to happiness. There is no quicker transport to the experiential realm and full engagement than through play, which brings together all the elements you want for the optimal moment.

Play is 100-percent experience. It's done for the intrinsic pleasure, for the participation. With no judgment or outcomes needed, play grounds you in the now.

Researchers say that the more absorbed we are in activities we like to do, the happier we are. Abraham Maslow and Mihaly Csikszentmihalyi pinpointed the power of full involvement in the moment to produce optimal experiences. Maslow called optimal moments the time when we are most attuned, "more integrated and less split, more perfectly actualizing." He argued that these instants of sublime activation had all the hallmarks of the religious or mystical but were triggered by intensely felt, secular experiences.

Linda Imle, a cyclist, computer technician and grandmother in Fairbanks, Alaska, told me that when she's on the road with her bike, "it's a coming together of mind, body and spirit. It's one of the highest of all highs." Imle cycled the entirety of Route 66, Chicago to Santa Monica, on her 66th birthday.

Contrary to stereotype, engaged play is the gateway not to time-wasting but to times that let you contact deeper realms. When you paint a canvas or play volleyball, you're in a creative improvisation that calls on inner fortitude and commitment and that reflect your values through self-expression. Play satisfies core self-determination needs, such as autonomy and competence, as little else can, connecting you with your mandate to explore and challenge yourself. That's the integration Maslow was talking about. You tap the true you, not the performance identity of the job or the presentation identity that we display to others. Play relieves you of the burden to be someone you're not. There's nothing on the line; it's just play. Just you.

When it comes to beefing up your happiness, it's hard to do better than engaged play. Not only does it align you with your deepest needs and deliver fun in the moment, but the social component of play is a huge predictor of increased daily well-being, the research shows. Participating in recreational activities has been connected to increased positive mood and experiencing pleasure. And play increases the odds that you're going to have more fun in your life because it's a huge stress buffer, reducing strain and burnout, boosting your immune system and pumping up vitality and energy.

When you're stressed, the brain's activated emotional hub, the amygdala, suppresses positive mood, fueling a self-perpetuating cycle of negativity. Play can break you out of that straitjacket. It also cut through stagnation at the office. Studies show that playfulness can increase performance on the job and stoke creativity by breaking up the mental set that keeps us stuck. It resets the brain.

This tonic we write off as trivial is a crucial engine of well-being. In its low-key, humble way, play yanks grownups out of their purposeful sleepwalk to reveal the animating spirit within. You are alive, and play will prove it to you.