The purpose of this question is to find out what you consider to be ‘challenging’, whether you can show a logical approach to problem-solving, and how you respond to and overcome difficult times. To portray yourself in a positive light, think of a situation which was not caused by you, and which you can quickly explain in a few sentences. Explain how you defined the problem, what the options were, why you selected a particular option, and what the outcome was and try to always end on a positive note.