One theory in psychology research suggests that we all have a happiness “set-point” that largely determines our overall well-being. We oscillate around this set point, becoming happier when something positive happens or the opposite, afterwards returning to equilibrium.

But this set-point, to a certain extent, can be reset. Although our general mood levels and well-being are partially determined by factors like genetics and upbringing, roughly 40 percent of our happiness is within our control, according to some experts, and a large body of research in the field of positive psychology has shown that happiness is a choice that anyone can make. As psychologist William James put it, “The greatest discovery of any generation is that a human can alter his life by altering his attitude.”

A little effort can go a long way in increasing happiness. Two small experimental studies, published this year in the Journal of Positive Psychology, found that simply trying to be happier could actually elevate mood and well-being. In one study, two groups of students listened to “happy” music — one group was instructed to make a concerted effort to feel happier, while the other group was instructed not to actively try to lift their mood. The group that tried to feel happy experienced the most elevated moods after listening to the music.

People who are happy choose to make happiness among their top goals in life, according to psychologist Tom G. Stevens, Ph.D. , author of You Can Choose to Be Happy.

“Choose to take advantage of opportunities to learn how to be happy. For example, reprogram your beliefs and values. Learn good self-management skills, good interpersonal skills, and good career-related skills. Choose to be in environments and around people that increase your probability of happiness. The persons who become the happiest and grow the most are those who also make truth and their own personal growth primary values.”

The secret to happiness could be as simple (and difficult) as becoming more mindful. Meditation — a practice that anyone can do, anywhere, so long as they’re willing to sit and try to silence the mind — is thought to be a happiness-booster. And people who meditate daily report feeling at ease with themselves.

University of Wisconsin psychology professor Richard Davidson found in his research that a meditation practice might help to shift brain activity from the right frontal area of the brain (associated with depression, anxiety and worry) to the left, which has been found to correlate with feelings of happiness, excitement, joy and alertness.

Conventional thinking has it that pursuing success will lead to happiness, but research has shown that it may be just the opposite. Pursuing happiness leads not only to happiness itself, but also to success, according to Shawn Achor, author of The Happiness Advantage.

In his 12 years researching happiness at Harvard, Achor found that cultivating a positive mindset could boost well-being and improve workers’ performance on many levels, from productivity to creativity and engagement.

“People who cultivate a positive mind-set perform better in the face of challenge,” he wrote in Harvard Business Review in 2012. “I call this the ‘happiness advantage’ — every business outcome shows improvement when the brain is positive.”

So yeah it is a choice, but depression is also, and people sometimes chose to be depressed because that connects them with other people. Think about that.