Every single Investment Banking interview is going to ask the question - "Why Investment Banking?" and more specifically "Why this bank? / group?".
Let's be honest no one is ever going to say prestige, money, career aspirations, and you will never get the job if you say these things. Although they are definitely a huge part of the selling point of banking.
Most prospectives answer with some sort of bullshit along the following:
"I am good at math and am analytical" - this leads to follow-up questions like "tell me about a time you analyzed something" or "why aren't you an engineer then, we don't use that complex math?"
"I have an interest in finance and the markets" - this leads to the interviewer asking "why are you interested in finance?" as well as asking in-depth questions about the markets and then people getting screwed because they really don't know the markets that well and also why they don’t want to be a trader instead. Investment Bankers aren't as interested in the markets...
Pretty much these answers are bullshit for most....
True Love for Finance
For the few people who actually do have an interest in finance, and get a high reading deal announcements they don't need coaching for this answer. It's easy to answer "why IB?" when you love finance and can talk about it like second nature.
"I read Barbarians at the Gate when I was in High School and knew I wanted to be involved in M&A. I started following DealBook and following every deal announcement and joined every finance club at my school and do modeling case competitions for fun.".
For the rest of you reading this who don't genuinely love finance its hard to explain that you are an ambitious person looking for money, prestige and exit opportunities.
That's why you should focus on the non-finance aspect. The People.
Bankers pride themselves on their work ethic, their ability to learn new things quickly and their expertise in certain areas. If you don't love finance, focus on how you want to surround yourself with these types of people.
"I have spent a lot of time exploring careers in finance talking to people in Sales and Trading, in Wealth Management, in Consulting, and in Investment Banking. I particularly felt most at home with those in Investment Banking because I found they were type-a personalities who have a desire to learn and do whatever it takes to succeed and are willing to bust through walls for 80 hours a week to get there.. I want to work with people like that and like the people I have talked to and met at here at [insert bank/group you are interveiwing with here]."
This answer is perfect because of the fact that it shows that you did your homework learning about careers, and getting to know investment bankers. It also shows that you respect the person interviewing you without directly being a kiss-ass. Finally, it shows the kind of personality you relate with and the type of person you want to be....The only follow-up will be to tell them who you spoke to at that specific bank. Be prepared and make sure to have had conversations with a few people from the bank/group before your interview.
The absolute best case-scenario is if you have a love and genuine interest in finance and also know who you want to work with. Meld both the love for finance response and the discussion on the people.
Investment Banking is so different in terms of day-to-day work from anything else in high finance that bankers want to know that you are the right fit for it more so than your passion for finance. Investment Banking like any career is built on people. Finance is not rocket science and anyone can learn it, but personality and work ethic is not something that can be taught.