Below is a link to a blog I would encourage you to read.  I really like the question - "Tell me the last time you failed at something professionally."  It is ok to have failures, it is what you learn from them that counts.  Think about the failures you mighe have had in the past and how you learned from it and what you would do differently going forward. 

 

http://www.ere.net/2013/03/14/the-magic-interview-question-have-you-failed-in-your-career/