Often candidates prepare themselves so much for particular questions that they are eagerly ready to respond. Slight re-wording of a question however, can alter the question entirely. I have heard many candidates respond inappropriately to a question because they did not listen carefully to the entire question.
Perhaps they heard the question they wanted to hear and prepared for, or only heard the beginning of the question and immediately started playing the tape in their head.
As a result they did not answer the question that was actually asked. When preparing for specific interview questions, play around with different versions...questions that are similar, but different. The following is an example.
These are 5 different questions and should have 5 different responses.
1) Why do you want to be a firefighter
2) Why do you want to be a firefighter for the city of ____
3) What made you decide to be a firefighter
4) What first triggered your interest in the fire service
5) What is the single most appealing aspect of being a firefighter
Always listen to each question carefully and make sure your response is appropriate and answers the question that was asked.