To be successful at Fannie Mae, you should have strong personal motivation to succeed, and your interviewer is asking this question to see what makes you tick in your career. In your answer, you might include an anecdote that explains why you got into the finserv and the housing industry in the first place. Perhaps a previous manager has even commented on your motivation, which you should certainly include in your answer.
While great benefits and solid work-life balance may be all motivators in pursuing a career with Freddie Mac, don't focus on these aspects in your answer. Instead, focus your answer on intrinsic motivation mostly removed from external factors like money, status, or external validation.
