How do you stay enthusiastic / passionate through the grind/boring times while working at your investment banking job?

This is a question I'm going to need to address on an upcoming IB interview. One thing they've said about me is that they can tell I have a lot of passion and enthusiasm for the field and in particular this job. They want to make sure that I'll be able to keep this attitude even through the grind times. For those in the field, how do you do it? All respondents are welcome, no need to be in the field, what are some ways you would think to answer this question?