To be successful in any interview setting, you will have to master both your known interests and what I refer to as developed interests. Known interests are those interests which you have at the outset of your job search. Developed interests are those interests that you work to develop, and that naturally develop, in the course of preparing for (and even in the midst of) your interview.
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Known interests tend to accrue and change throughout the course of one's career. They are experiential in nature. Thus, a second-year law student applying for summer associate positions is likely to have fewer known interests than a third-year associate or a partner with 12 years of experience. In either case, before beginning your job search, you should take the time to ascertain the full scope of your known interests and limit your search to prospective jobs that meet those known interests.

For example, imagine that you are a second-year corporate associate at a large, well-respected law firm in New York. You decide to move to Washington, D.C. and have determined, over your first two years of practice, that you have a particular interest in mergers & acquisitions. At the outset, before you even begin your job search, you have certain clear known interests. Your known interests include, among other things, your interest in moving to Washington, DC, in practicing at a law firm, and in gaining experience with mergers & acquisitions. Upon reflection, you may discover additional known interests that you were not previously aware of. For example, after giving it some thought, you might realize that you prefer to practice in a small or medium-sized firm, or alternatively, you may determine that you have appreciated the resources made available to you in a larger firm setting and thus want to limit your search to similarly-sized firms.