The reason I picked this as the most difficult question because I wasn't sure how they wanted me to answer the question. I believe they wanted me to say yes this was an unfair interview, you kept asking me the questions over and over again trying to get me to change my answers. I on the other hand was polite and said that I don't believe the questions you have asked me provides you with an overall perception for the type of knowledge and skillset that I have. This is your interview and it is fair for you to conduct it as you see fit.