Each of us knows at least one. I mean someone who inevitably makes you feel happier, more inclined to do something nice for the next person you meet, just by spending a few moments in their presence. Someone who radiates simchas hachaim.

Simchas hachaim bears no resemblance to the hale-fellow-well-met jocularity of a successful politician – an external garb. It is a quality that wells up from within and is incapable of being contained within one body, but must burst forth and be shared with others. It is expressed in a warm smile, a natural inclination to judge others favorably, optimism, and a strong desire to help others.

Take my former optician Mr. Rosenberg, for instance. I never saw him without a gentle, knowing smile on his lips. And he never showed any sign of pressure, even when someone who had not purchased glasses from him came in looking for a tiny screw to hold the earpiece. He would just take out his plastic box containing hundreds of such screws and patiently try one after another until he found the right one. Then he would inevitably waive payment, even though fiddling with a series of tiny screws would be an ordeal even for someone whose fingers were not in their seventh or eighth decade.

Those rare individuals whose simchas hachaim never deserts them play a vastly disproportionate role in our society. Like a rock hitting the water, they send off waves of positive energy in every direction. Social scientists have begun to confirm this insight. A new study in a leading British medical journal describes how much of our emotional state is collective – i.e., determined by the emotions of those around us, even those from whom we are two or three degrees removed. One person’s happiness triggers “an emotional riot,” says Dr. Nicholas Christakis of Harvard Medical School.

Those who radiate simchas hachaim also serve as constant reminders of a vital lesson: simchah is a condition of the soul, not the product of our external circumstances. There are Holocaust survivors and others who have experienced terrible personal tragedies, whom one would assume upon meeting them for the first time, had lived idyllic lives. And there are those who can barely function if they have a hangnail. Neither the happiness of the one nor the irritability of the latter can be explained by the circumstances of their lives. The more we recognize that the external events of our lives do not have to determine our emotional state, the less likely we are to fall into the role of passive victims.

I NEVER MET MRS. SIMCHAH VAKNIN. I first heard of her only when she was killed in a tragic car accident, when a young Arab driver plowed into the car, in which she was accompanying her daughter-in-law to the hospital, to deliver a baby. (The mother and baby survived.) My sister-in-law Channah had, at that point, worked for three months in the health clinic in Jerusalem’s Ramot Dalet neighborhood, where Mrs. Vaknin was the head nurse. And after Simchah’s sudden death, she felt a tremendous need to talk about her to overcome her deep sense of loss.

Channah’s first three months in the clinic should, in the normal course, have been ones of high tension. She was starting her first job, after having gone through nursing school in middle-age and with a large family. But instead they were the months of her greatest personal growth because of Simchah’s example.

Simchah was always available to consult and advise both patients and co-workers. And a new nurse had plenty of questions. When called at home, she invariably assured the caller that talking was no inconvenience, as she was just hanging up the laundry and could carry on while talking.

Simchah truly embodied her name – k’shma kein he. Despite the pressure of a busy clinic, she was incapable of losing her good cheer. When people came after the scheduled hour for taking blood tests, she might offer a mock scolding, but it was inevitably followed by a big smile and the blood being taken. She had no fear of being taken advantage of, and was not.

Her forgiving nature extended not only to patients but also to those who worked under her. If a patient complained that one of the other nurses wasn’t “nice like you,” she would immediately sing that nurse’s praises, and assure the disgruntled patient that any gruffness he or she had experienced, was totally out of character and surely the result of extenuating circumstances.

She created an atmosphere that every visitor to the clinic immediately sensed. Channah is constantly being approached by strangers, who ask her, “Aren’t you a nurse in Simchah’s clinic?” and want to share some story of a kindness Simchah did for them.

A story told by her sister at the shiva house captured Simchah’s positive approach to everything. The sister lives on the ground floor of an apartment building, directly underneath a very rough family. The upstairs neighbors have an unpleasant habit of throwing their garbage out the window, into the sister’s garden. Every time that would happen when Simchah was visiting, she would immediately attribute the behavior to young children who did not know better. Then no matter how distasteful the garbage, Simchah would rush outside to pick it up, before her sister exploded and invited the neighbors to come downstairs and clean up their mess.

The impact of even brief contact with Simchah could be life-changing. “The most important lesson I learned from her,” my sister-in-law tells me, “is that you don’t lose by giving. Everybody is always afraid of being taken advantage of, or of not being professional. Simchah didn’t have that fear, and she was the happiest person I ever met.”

“What would Simchah have done?” Channah finds herself asking all the time – most recently when a family of nine trooped in for flu shots ten minutes before closing, after having been told the closing time, and that the nurse must remain with the patient for half an hour after the shot.

And when Channah arrived home a half an hour late, with the car that my brother was waiting for, she was surprised to find him completely calm. Even though he never met Simchah, he too has learned to ask the question: “What would Simchah have done?”