The story is told of two monks, one young and one old, that embarked on a long hike across a hot desert to reach their monastery. The younger monk was stronger and faster and arrived first, having suffered through the long barefoot walk with his feet severely blistered and burned. His fellow monks tended to his injuries and prepared for the arrival of the older monk who would, they reasonably expected, require similar care.

When the old monk arrived, however, he had no injuries whatsoever. In fact, he was smiling and happy. The young monk was shocked. “How did you survive the blazing heat when I suffered so greatly?” he asked. “Did you use magic to cool the desert sands?”

The old monk smiled kindly and pointed to the sandals on his feet. “I knew that I could not change the desert, so I changed myself,” he said.

The older monk knew something that the other did not. Even when faced with an imperfect, hostile world, happiness is still possible. Changed practices and habits will change outcomes and results. The old monk could literally walk on burning sand and remain untouched by pain or sorrow. He knew the game-changing secret of happiness.

Mahatma Gandhi reminded the world of this simple truth when he said, “If you want to change the world, start with yourself.”

Shakespeare also understood the value of self-determination and wrote, “There is nothing either good or bad, but thinking makes it so.”

John Milton long ago explained the force of conscious choice in the creation and destruction of happiness, noting, “The mind is its own place, and in itself can make a heaven of hell, a hell of heaven.”

Fortunately, science, philosophy and human experience have identified the habits and practices most likely to produce the happiness that everyone seeks. Each one is a true game-changer.

First, forgiveness. Psychologists define forgiveness as a deliberate release of resentment against a person that has caused one to suffer harm. Mother Theresa called it an act of love, and Gandhi called it an act of strength. Contrary to popular opinion, forgiveness is neither amnesia nor amnesty. Forgiving an injury is not the same as forgetting it occurred or deciding it was really not so bad after all. Instead, it is the intentional letting go of anger and hatred, refusing to remain a victim of whatever and whomever caused the harm.

Science has proven that unforgiven resentment is unhealthy, including higher levels of sadness and anxiety. Dr. Everett Worthington, a leader in forgiveness research, found that withholding forgiveness increases a person’s levels of cortisol, a hormone linked to heightened stress and a weakened immune system. Forgiveness makes people feel more in control of their own lives and less dominated by those that have hurt them. The person forgiven remains as untouched by the forgiveness as they were by the original resentment.

Next, gratitude. Scientists define it as the appreciation of what is valuable and meaningful. We can think of it as a genuine, thankful awareness of whatever good things life gives us. What one scientific study after another recommends is the habit of focusing on the aspects of present tense existence that are good right now with an appreciation of whatever it is that makes them good. Dr. Robert Emmons, the world’s leading researcher on gratitude, calls this a “felt sense of wonder, thankfulness and appreciation for life.”

Rabbi Harold Kushner calls it finding “the holiness in those things you take for granted.”

Either way, the rewards are undeniable. Psychological experiments have proven that people who practice gratitude have a greater sense of emotional well-being, enjoy more positive emotions, have better relationships and are more compassionate. Even their physical health is better. In short, they are happy.

The Pulitzer Prize-winning playwright Thornton Wilder agrees with the scientists, saying, “We can only be said to be alive in those moments when our hearts are conscious of our treasures.”

Thankful practices may include the use of a gratitude journal in which the grateful person writes down everything they can think of that makes life good or even tolerable at that moment and resolves to be thankful for each one. Some people find value in writing a letter or even a short note to someone whose impact on life has been positive and bright. Others simply think or pray or meditate about the objects of their gratitude. Nearly 2,000 years ago, the ancient philosopher Marcus Aurelius understood the value of gratitude, writing, “Take full account of the excellencies which you possess and in gratitude, remember how you would yearn for them if you had them not.”

Entertainer Willie Nelson concurs: “When I started counting my blessings, my whole life turned around.”

Finally, optimism. Scientific researchers define optimism as the practice of interpreting current situations in the best possible light and believing in a future of good, positive experiences. Helen Keller, who certainly had just cause to see her glass as half-empty, called optimism “the faith that leads to achievement.”

Not only does optimism lead to happiness, but it is also more realistic than pessimism. The definition of optimism is the tendency to interpret current situations in the best possible light. Optimists do not wildly romanticize the world around them; that is what idiots do. Optimists know that even in a world where bad things happen, marvelous things are also bound to happen. Looking forward to good things and refusing to be crushed by the bad is neither foolish nor naive.

As the Dalai Lama has put it, optimism simply “feels better”.

The groundbreaking psychologist William James said, “Why should we think upon things that are lovely? Because thinking determines life.”

Even better, optimism is good for you. Harvard researchers have proven that optimistic heart surgery patients have better outcomes. Other studies have shown that optimism correlates to reduced blood pressure, better mental health, decreased levels of stress hormones, improved immune function and all-around wellness. Nobody lives forever, but optimists live the longest.

Facing the future with positive expectations is also consistent with cutting-edge findings about human nature. The eminent memory scientist Elizabeth Loftus has proven that no one can really be certain that they remember the past accurately. If a person cannot be sure of the past, which has already happened, there is certainly no reason to believe that anyone can know the future. Therefore, because the future is uncertain, the smart, healthy, lovely and happy choice is to practice optimism.

Forgiveness, gratitude and optimism: Three surefire practices for the person that wants to change their world.

Spero Lappas, Ph.D., is the author of Conquer Life’s Frontiers, A Philosophy of Individual Fulfillment, available at ConquerLifesFrontiers.com. This article is adapted from his upcoming book The Twelve Names of Happiness to be published in the spring of 2019.