Former U.S. president Abraham Lincoln once noted that “Folks are usually just about as happy as they make their minds up to be,” and over 100 years later this observation still rings true. A recent study suggests while happiness rates in young adults and teens are on the rise, happiness in those over 30 is falling. However, in order to figure out what’s behind this decline, we must first understand the key elements to happiness.

In a recent study, now published in Social Psychological and Personality Science, a team of researchers led by Dr. Jean M. Twenge, author of Generation Me and professor of psychology at San Diego University, investigated how happiness among Americans had changed in the past 40 years. In their research, the scientists analyzed data from four nationally representative samples of 1.3 million Americans aged 13 to 96 taken from 1972 to 2014.

Past research has shown that older individuals are generally happier than the young, but results revealed that starting in 2010, this trend no longer existed. For example, around 38 percent of adults older than 30 had reported being “very happy” in the early 1970s, but by the 2010s this had shrunk to only 32 percent. In comparison, 28 percent of adults aged 18 to 29 said they were “very happy” in the early 1970s, and 30 percent reported the same in the 2010s. Teen happiness also appeared to have increased in the past 40 years, with 19 percent of 12th graders claiming to be “very happy” in the late 1970s versus 23 percent in the 2010s. This pattern was seen in both men and women.

Twenge told Medical Daily in an email that although she can’t say for sure what caused these changes in happiness, cultural changes that occurred at the same time as happiness shifts may be related. According to Twenge, modern American culture greatly emphasizes reaching for the stars and following your dreams, ideas that can help elicit hope and optimism in the youth. Once these young adults age, however, this optimism quickly diminishes.

“The average mature adult has realized that their dreams might not be fulfilled, and less happiness is the inevitable result,” explained Twenge in a statement. “Mature adults in previous eras might not have expected so much, but expectations are now so high they can't be met.”

The prevalence of technology, attention-seeking behavior, and quick fleeting romances that brought individuals excitement in their youth “may not provide the stability and sense of community that mature adults require,” Twenge said. In addition, marriage, a behavior consistently correlated with happiness, is at at an all time low.

Twenge is not the first to note the relationship between happiness and expectations. A 2014 study on happiness found that having money and success did not increase happiness as much as lowering expectations did.

“Lower expectations make it more likely that an outcome will exceed those expectations and have a positive impact on happiness,” lead researcher Dr. Robb Rutledge, explained, as reported by TODAY Health and Awareness.

In addition to unfulfilled expectations, new parenthood experienced by many adults aged 30 and over has also been associated with rapid decreases in overall happiness. A 2015 study conducted by researchers at the Max Planck Institute for Demographic Research in Rostock, Germany reviewed the responses of about 20,000 new parents and found that many experienced a sharp increase in happiness shortly after the birth of their child, followed by a steady decline.

While the problem may seem overwhelming, Twenge suggests that increasing happiness may be relatively simple.

“One of the most popular is to practice gratitude — to be grateful for what you have instead of always thinking about what you don't have,” Twenge wrote to Medical Daily in an email. “That might help mitigate the effects of high expectations.”

Twenge also suggested that prioritizing relationships by spending time with friends and family is also an easy way to increase personal happiness.

Source: Twenge JM, Sherman RA, Lyubomirsky S.More Happiness for Young People and Less for Mature Adults Time Period Differences in Subjective Well-Being in the United States, 1972–2014. Social Psychological & Personality Science. 2015.