It's true: What doesn't kill you will make you stronger. To a point.Beth Elliott nursed her mother through the last stages of cancer. Less than two years later, her husband learned he had only a few months to live. Six months after he died, Elliott herself was diagnosed with thyroid cancer.What would you do if you were her? Succumb to grief and feel unable to go on with your life? Or find a way to cope and move on? Elliott, 40, a college student in Hampton, Va., says she eventually realized she had "a choice between life and happiness or letting this get me down and staying miserable."Adversity and ResilienceIt turns out the adage is true: Some adversity in life makes us stronger -- or, at least, better able to handle everyday hassles. But only up to a point.A recent study monitored the mental health and general well-being of nearly 2,000 people for several years, checking on them via online surveys. They were asked to list any troubling events, such as divorce, loss of a parent, or a natural disaster, that had happened to them before the survey began. They also reported adverse events that happened during the survey period.The surprising result? Those who had previously endured hardships were happier afterward. They were tougher, in a good way."People who are never challenged by life don't have the opportunity to learn how to overcome adversity, which enables them to develop coping strategies, identify who the important members of their social network are, and feel competent after they make it through," says Roxane Cohen Silver, PhD, the University of California, Irvine, psychologist who led the study.When there's too much adversityIndeed, while everyone responds differently to tragedy, those in the study who had never undergone hard times tended to have less of a sense of general well-being.After tragedy, most of us eventually do return to our previous state of well-being. But there's a limit. Too many negative events can overwhelm a person's ability to cope. In the study, two or three misfortunes seemed to enhance resilience, but having as many as 15 stressors hindered daily coping.Before his death, Elliott's husband spoke to her many times about her future. These conversations built her emotional strength. "All that has happened to me has given me a gift to see how strong and capable I am," she says.