Happiness - you know it when you see it, but it's hard to define.
You might call it a sense of well-being, of optimism or of meaningfulness in life, although those could also be treated as separate entities. But whatever happiness is, we know that we want it, and that is just somehow good.
Research suggests that genetics may play a big role in our normal level of subjective well-being, so some of us may start out at a disadvantage. On top of that, between unexpected tragedies and daily habitual stress, environmental factors can bring down mood and dry up our thirst for living.
Being able to manage the emotional ups and downs is important for both body and mind.
Why be happy?
Many scientific studies, including some by Kubzansky, have found a connection between psychological and physical well-being.
A 2012 review of more than 200 studies found a connection between positive psychological attributes, such as happiness, optimism and life satisfaction, and a lowered risk of cardiovascular disease. Kubzansky and other Harvard School of Public Health researchers published these findings in the journal Psychological Bulletin.
Happiness: Living in the moment
But what about right now -- what can we do to make ourselves feel more positive?
If you're seeking to increase your own sense of happiness, try mindfulness techniques. Mindfulness means being present and in the moment, and observing in a nonjudgmental way, Susan Albers, psychologist at the Cleveland Clinic, told CNN in 2010.
Can mindfulness help manage pain and mental illness?
Mindfulness comes from Buddhism and is key to meditation in that tradition. Therapies for a wide variety of conditions, including eating disorders, depression and PTSD, incorporate mindfulness. Focusing on the here and now is a counterbalance to findings that mind-wandering is associated with unhappiness.
So remember: A glass half full might be healthier than a glass half empty.
By Elizabeth Landau, CNN