This is another question used in the job interview to try and gauge a response from the candidate on the spur of the moment. Regret is a powerful concept and very emotionally driven.

People could have strong regrets and may make the mistake of spilling out their experiences that are not appropriate in the job interview. Alternatively we all have regrets and should not say we do not have any. You come off looking fake.

Answer this question by explaining a situation you have no control over but that things could have turned out better. It may have been a decision or action taken by someone else that had an effect on you.