Why can't "The truth is, I still don't know what I want to do with my life, and it's likely I'll spend the next few decades trying to find out. But what I can promise you is this: I will work hard, and I will work the necessary long hours. I will give you my best as long as you give me the opportunity to prove that I can do this job" work as an interview answer?

I don't have any long-term career objective. At least, not in the sense that I have my whole future mapped out and know exactly how to get there. And yes, what I'm doing now is nowhere near my my idea of an ideal job, but I don't mind that I'll most likely never get that dream job. What I do know is that I enjoy certain aspects of what I do now and as long as I'm working alongside a good team of people, it's likely that I'll stay there long enough for you to get way more than your money's worth out of this workaholic.