After a decade of interviewing and studying more than 1,000 workers — from Fortune 500 CEOs to Chipotle kitchen managers — Harvard researchers found that employees who quit their jobs mainly do so because they aren’t making the progress they seek in their careers and lives.

The findings are detailed in “Job Moves,” a new book co-authored by Michael B. Horn, a lecturer at the Harvard Graduate School of Education; Ethan Bernstein, a professor at Harvard Business School; and Robert Moesta, CEO and founder of consulting firm The Re-Wired Group.

Quitting and switching jobs, the authors argue, has little to do with career progression as it’s traditionally defined — a steady, linear ascent up the corporate ladder. Instead, the authors say, the progress that matters is the intersection of what a person seeks in both their professional and personal life, a definition that can evolve over time.