If you always prepare for the worst, you’ll never be disappointed, right? You’ll never feel discouraged by a layoff, betrayed by a friend, or set back by an illness because you saw it coming. After all — pessimism is just another name for realism.

Ah, such a crusty, unnattractive outlook! And it can be a self-fulfilling prophecy.

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“Pessimists spend so much time focusing on the worst, they unintentionally invite the worst instead of promoting the best,” said Dr. Joffrey Suprina, dean of the counseling, psychology, and social sciences department at Argosy University in Sarasota, Florida.

Suprina counsels people with chronic pain that’s been unsolved by medical interventions. “What you focus on is what you will encourage,” he told LifeZette. People with chronic pain literally feel more pain when they’re pessimistic. “You will actually see chemistry happen in the brain that will augment the pain. When people can be distracted and think about something more positive, when they watch a comedy or find a way to laugh, those aches and pains will diminish.”

So what’s going on in your head can have tangible consequences.

One study in Finland showed that people with coronary heart disease had higher levels of mortality when they had a pessimistic outlook, even when researchers controlled for severity of disease. Pessimism seems to take a toll on heart health in particular. Optimism, on the other hand, has been shown to reduce blood pressure, keep people healthy longer, and increase the possibility of professional success.

“Only 10 percent of our long-term happiness is based on external factors. The remaining 90 percent is based on how we process life events and circumstances,” said the U.S. surgeon general.

Optimism has also demonstrated powerful results even with severe disease like cancer. Patients who wake up with a grateful attitude and who feel glad to have another day to live encourage health and well-being in their lives, said Suprina. In these cases, “perception is more important than fact, especially when it comes to the psychology of the brain.”

“Only 10 percent of our long-term happiness is based on external factors,” said U.S. Surgeon General Vivek Murthy at the Aspen Institute in Washington, D.C. “The remaining 90 percent is based on how we process life events and circumstances.”

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Gratitude, exercise, kindness, meditation, and social connection can be used to cultivate happiness purposely, said Murthy. For people who are perpetually pessimistic about life, Murthy suggests that noting something they’re grateful for right before bedtime is a good idea. They could also change their schedule to allow time to sit down with family members for dinner or take 15 minutes during a lunch break to get exercise or meditate in a quiet corner of the room.

Related: Lose the Bad Attitude for Your Own Good

Perennial pessimists must cultivate positive thinking to overcome bad habits. “Optimism is a skill that some come by more naturally,” said Suprina. He teaches his patients to “reframe” things in their lives that they view as bad. For instance, if a father is frustrated with a stubborn teenage daughter, Suprina helps him see how stubbornness can come in handy for teenage girls — when they need to set healthy boundaries with boyfriends, for example.

Suprina mentions the yin and the yang — there’s a dark spot in the white portion and a white spot in the dark portion. Pessimists tend to focus on the dark spot — while missing all the bright portions of their lives. “Things are not black and white, all or nothing. There are pieces within each circumstance to admire.”