When golfer Bubba Watson won his first major tournament -- the 2012 Masters -- the shaggy-haired Floridian dropped his head on his caddy's shoulder and sobbed. On Sunday when Watson claimed his second green jacket at Augusta National, his caddy's shoulder was again subjected to a drenching.

Tiger Woods, one of the fiercest competitors in sports, wept profusely after winning the 2006 British Open. Fellow golfer Fred Couples hid his face behind his visor when he lost complete control in a TV interview after winning the 2003 Shell Houston Open.

What's this about? Why do people cry tears of joy?

It's not just golfers, by the way, and it's not just athletes. Weddings, graduations, even sometimes sex -- there are a variety of joyous occasions that perplexingly turn on the tears, a physiological response predominantly associated with pain, sorrow and loss.

Ad Vingerhoets has been studying crying for years, one of few academics in the field.

"It's a lonely business," admits Vingerhoets, a professor of clinical psychology at Tilburg University in the Netherlands.

He says the way humans cry and the triggers that turn on the waterworks differ greatly depending on the stage of life a person is in.

For helpless infants, crying is a way to communicate distress to parents. It is necessarily loud, a characteristic that changes over time. The older one gets, the less noise one makes while crying.

Vingerhoets says regardless of age, humans cry in response to powerlessness and to loss or separation. But where children and adolescents will cry in response to pain, tears as a reaction to physical pain are less commonly seen with advancing age.

Instead, adults cry about things that move them, evoke their empathy or sympathy, appeal to their sense of morality or sentimentality.

Children don't cry when they hear about someone losing their life to try to save someone else, but an adult might. Similarly, a beautiful piece of music might bring tears to adult eyes but would be unlikely to do so to a child's.

At the heart of that type of reaction may be a type of powerlessness, Vingerhoets suggests. People who are overwhelmed with emotion -- even positive emotions -- can have trouble processing the flood of feelings. Tears provide a release.

"You don't know how to express your emotions and you're really overwhelmed," he explains.

He suggests that the athletes who cry after winning are often dealing with complex emotions. For instance, they may have affected a career comeback after overcoming adversity.

He points to a Dutch cyclist, Leontien van Moorsel, who cried after she won a gold medal at the Summer Olympics in Athens in 2004. She had been a successful competitor but developed severe anorexia. Her win in Athens came after she battled back from the eating disorder.

Some find their victories tinged with other complicating emotions. Couples won the 1992 Masters and several PGA events in the 1990s, but had gone several years without a victory. He admitted he had been afraid he'd never win again.

And Woods' uncharacteristic collapse into tears came at the first major tournament he won following the death of his father, Earl. He said later his emotional response stemmed from the sadness he felt that his father, a dominant force in his golfing career, wasn't there to see him win.

Watson, who famously said he never dreamed he could win an event like the Masters, claimed his first just two weeks after he and his wife adopted their son, Caleb. Angie Watson and the baby were not with him at Augusta for his first victory; on Sunday Watson quickly scooped Caleb, now a toddler, into his arms after winning, carrying him to the clubhouse where he recorded his winning score.

"Those people cry when they win who have had problems before," says Vingerhoets. "They had difficulties to qualify themselves for the Olympic Games. They were severely hurt or wounded and it was doubtful (they could compete again)."

By contrast, one rarely sees tears in the victors who expect to win. "The usual winners, I think it's far less likely that they cry."

Social bonding can also lead to tears in adults, Vingerhoets says -- things like hearing one's anthem played at the Olympics.

Canadian freestyle skier Justine Dufour-Lapointe was the picture of exuberance after winning gold at the Sochi Olympics. But after she received her medal and watched the Maple Leaf rise to the strains of O Canada, tears rolled down her cheeks.