Behavioral interview questions are uncomfortable. I've preached that over again on this blog. The more comfortable you get answering them, the better you'll be able to handle the unexpected.
How would you answer this question: Tell me about an objective in your last position that you failed to meet, and why.
No one wants to admit to failure. Pick one that was not essential to your job. Use your STAR (situation, task, action, result).
It is good to add what you learned from this example, and what you would differently the next time, to ensure that you did meet the objective or quickly resolve the problem.