One factor is people's natural progression through three career stages identified by Carole Kanchier, a career coach and author of Dare to Change Your Job and Your Life. In the entry stage, workers­ are excited to be learning new tasks and skills. After a while, they've mastered the job enough to feel confident and productive. However, if they're not presented with new challenges, people get bored and enter the final stage. "You're disengaged. You lose productivity, and your confidence plummets," Kanchier says. For some people, switching companies can't compare to the excitement of learning a completely new trade.

"Oftentimes," she says, "the disengagement stage parallels the transition stage of a life cycle. Marriage, a crisis in a relationship, or a death in the family can trigger the need for a change. We begin to realize that time is finite."

In 1994, Debbie Gisonni faced family tragedy at the height of her career, when her mother, father, younger sister, and aunt died within a year of one another. During that awful time, the former corporate computer sales executive was made publisher in charge of launching a technology trade magazine. "I immersed myself in work and more money, more responsibility, more powerful positions," she says.

Then it hit her. At 37, she was getting sick all the time, and she had no more enthusiasm for her work. "Life was so short," she realized. "If I was going to do something more meaningful, now was the time." She walked away from her career with no idea of what to do next.

To come to terms with her grief, she began to write about life and loss and moving on. That work became a book, Vita's Will, published in 2001. Now, Gisonni writes a column, gives workshops, and does one-on-one counseling, helping others­ find mission and meaning in life. Her next book will be Goddess of Happiness. "This whole thing started around death and dying," she says, "but a whole new lighter and happier side of me emerged. I realized that happiness is the one thing people want most out of life."