Carrots and sticks have long been the favored tool for business managers looking to motivate their workers, whether it’s to encourage with the promise of a raise, or to threaten with firing.

But a new study from the University of Iowa suggests that an employee’s personality is also a strong motivator of an employee’s behavior. Mick Mount and Ning Li, management and organization professors in the University’s Tippie College of Business, note that a growing body of evidence suggests that if a worker’s personality doesn’t fit the job requirements, he or she will not be motivated by external factors, no matter how tasty the carrot or painful the stick.