I was told by the interviewer all about how difficult and demanding the job was, and I was then asked in an almost perplexed way why it was I would even want the job. This is to make sure you know what you are getting into and they can be sure you will rise to meet the challenges. Tactic to weed out the unsure that may be a waste of their training expenses. Be confident. This is a job where the harder you work - the more you make, so be sure to emphasize that you understand that and are motivated to make the most you can for you and possibly your family.