"Tell me about a time you failed to complete an assignment on time."
If you are a good worker, then you probably haven't failed to complete an assignment on time. But if you have a lot of experience, you might have some situations where external factors caused you to miss a deadline. This is what my example will be about. But if you have an example where you failed to complete an assignment, make sure you give clear reasons why you failed and what you learned from it. Also, if you can't think of any, then use an example from your university days stating. But if you do, make sure you tell them that so far in your job experience, you completed all assignments on time or ahead of schedule.
Short Answer
"One time, I had a project that was due on Tuesday. On Friday I analyzed our progress and I was ahead of schedule. I didn't have to work over the weekend to complete the assignment. On Monday, my manager was sick so I had to attend several meetings that took all day. Because of that, I didn't complete my assignment until Wednesday. Now, I try to finish my assignments a day or half a day early because something unexpected could come up."
Long Answer
"With proper planning and good execution, I think it's hard to fail at meeting a deadline. But I remember one time in the middle of the project, our clients wanted to change one aspect of the assignment that we already completed. I analyzed the change request and told them that we wouldn't be able to make the date. I estimated that it will take three additional days. They insisted that we finish on the agreed upon time schedule. I told them we'd try but could not promise anything. Even with hard work and overtime, we missed the due date. We did however, finish one day late. In this situation where I didn't feel we could reach the deadline, I specifically told them that we couldn't, I continually sent updates on the progress to keep the clients informed. Since we missed the deadline, they were not too happy, but overall they were satisfied because I effectively communicated the progress regularly."
I like this answer because they want a situation that should make you look bad. Instead, you gave them a scenario where you failed to complete an assignment, but really it wasn't your fault. In the end, this answer makes you look good because you did everything right from communicating properly, giving them a new time frame, and reaching the goal two days ahead of schedule despite missing the original date by one. But just in case they ask what you could have done better, you can say something like,
"I feel I should have been more firm with the three additional days I requested. I like to meet difficult deadlines, but I knew the additional work was too large to finish on time."