Tell me about a time when you were unable to meet a project deadline. How did you react?

Nobody is perfect! The interviewer knows that there will be times when deadlines are not met and projects go sideways. What they want to know is how you are going to react. Explain how you can humbly accept responsibility and keep plugging away, despite the perceived failure.
Perhaps you underestimated the depth of the project, or maybe you faced a distraction at work. Whatever the situation was, discuss what you learned from the outcome. Show the interviewer that you do not have a defeatist mentality.