I don't remember what my answer was but I want to give some advice. They are looking for honesty (admitting you are human and that you make mistakes) and growth (you have the ability to learn from your mistakes and the humility to own up to them). So think of time either professionally or educationally that you made a mistake, give details, explain what you did to correct the situation and end it with a positive! Say that you learned to ask for more direction next time or something along those lines. Whatever the situation, make your mistake a POSITIVE for the company!