DHL has a vested interest in improving its career satisfaction scores across the board. As they state on their website, "Our yearly Employee Opinion Survey recognizes your voice, and the voice of all our employees, allowing you to influence the way we move forward." They not only want to gauge how you cope with stress, but they're also interested in your professional conduct. They're also curious why you are interested in this position. Everyone has those unique triggers that cause dissatisfaction with the job. Talk to the interviewer about any factors that may deflate or discourage you in the workplace. They're testing to see if your personality fits the role.