Not an easy one this one. However, you could answer like this.....

• It was in a nonprofessional area, and has helped me develop persistence.

• I always have a plan B for anything I undertake, therefore I always have more than one way to react.

• Your question comes a little early in my career.

• I don’t really remember a specific example. I try to learn form my experiences.

• (Three pieces of advice: never use the word failure, limit your answer to less than twenty seconds, and once answered, ask a question quickly to change the subject.)