The term "Survivor" is a difficult word. You could be a survivor of cancer or a near death experience, or you could just be surviving a bad time in your life.
Usually when a person is going through a hard time or experience, they think of a person or place that they want to see again. They push on and live through the experience just so they can see that person or place or thing again- therefore making them a Survivor if they succeed.
A relative of mine survived depression and sexual harassment. She is now dead due to a car accident, however when she was alive, she explained how she pushed on through depression and the harassment. "I wanted to make my friends and family happy, and keep them that way." I what she said when people asked how she convinced herself not to commit suicide. "I wanted to see the people that I love the most again." Is the reason she gave on how she got through what happened to her.
As stated before, a multitude of things can help somebody survive. Faith and belief in a certain person, object, or group of people can make somebody determined to survive. When they succeed in surviving for any amount of time that makes them a survivor.