Most interview questions invite candidates to boast about their successes, but not every question is designed to explore your triumphs. You may be asked to describe a time when things didn't go according to plan, but the interviewer will not be scrutinizing your answer so much as the way you respond to their question. The best way to answer questions about previous failures was debated by job seekers on the Dice Discussions board. Surprisingly, many techies objected to interviewers even posing such a question, because it infers that they might be capable of committing an error.
Since all human beings make mistakes, and errors are part of the learning process, job seekers should anticipate questions about failures and prepare a few answers, before attending an interview. Accept ownership for your actions before talking about what you learned, so you can conclude your story on a positive note.
Failing to take responsibility for your errors or becoming indignant when asked to describe a failure, may cause the interviewer to conclude that you don't accept criticism well or lack the personal insight or confidence to admit your mistakes and learn from them. Remember this quote: "Show me someone who has never failed and I will show you someone who's never tried." Certainly you don't want to be perceived as someone who is unwilling to step out on a limb; so don't hesitate to describe your failures in order to reach new heights.