One of the toughest interview questions: "What is your greatest weakness?". Is "I'm a perfectionist!" really the best answer?
The idea that you should answer "what's your biggest weakness" in a job interview with something that's really just a positive trait ("I'm a workaholic!" or "I'm a perfectionist!") is something you'll hear often from career coaches. The truth is, just stop. Every interviewer everywhere has heard it before, and would rather you just be honest.
In reality, the "your greatest weakness" question is a place for you to show where you can—and would like to—grow once you land the position. Obviously you shouldn't go to an interview and say your greatest weakness is something that's core to the job you're applying for, but showing you have a little ambition and plenty of room to grow and learn new things is more valuable than trying to save face.