Much like with the greatest weakness question, being asked about your failed projects can be another way that interviewers catch their candidates off guard. It is highly important to avoid saying answers such as “but it wasn’t my fault” or “it would have worked if they had listened to me.” The interviewer is not interested in who was to blame, and does not aim to embarrass you on your past mistakes. What they are looking for is someone who is able to learn from their mistakes and have the experience and knowledge to ensure that the mistakes do not repeat themselves. Answering that you “don’t have any failed projects” could show that you lack experience, so it is best to avoid that answer too. Give the interviewer a concise story with an explicit conclusion that demonstrates your ability to learn.