What is "over-prepared" ?

IF you pull a Marco Rubio and start repeating your speech over and over its obvious. Be genuine

I don't believe you can over-prepare. This is what Victor Cheng had to say in his book.

The Problem of Being “Overprepared”

One of my blog readers recently asked me, “Can a candidate be too prepared?” My short answer is yes—and no.

For years, interviewers have complained about candidates being framework robots. The complaint is similar to the story about a child with a hammer who suddenly thinks that everything is a nail. Interviewers may characterize such candidates as “too prepared,” but what they really mean is that the candidates prepared so incorrectly and became so entrenched in what they had memorized that they basically stopped listening and thinking logically during the case. A case interview is a thinking game, not a memory recall game. The process of mindlessly memorizing and recalling a frame is something I call framework vomit. All you do is swallow a bunch of frameworks in preparation for a case interview and then vomit them all back up during the case, regardless of whether they actually work for that specific case.

The key is to listen to the answers you get to the first few of those 15 questions, think about what is happening (formulate a hypothesis), and then decide if continuing with a certain framework would be useful. Remember, a framework is just one tool in a candidate’s tool kit.

If it is the only tool candidate uses, then she will come across as too prepared*

I did 100+ cases before I got the McK offer. I don't think you will be over-prepared, but you do feel that you are not making notable progress after 60 cases. That's because you know what's the right structure/approach to different kinds of cases by then. But you should continue practicing the cases, this will keep you sharp during the interview. What's more important, when you can comfortably solve the case, you will be able to focus more on developing your own structure and style based on the type of the case and the personality of interviewer you will be dealing with. These details also take a long time to practice, and you can always make it better. I think those who 'over practiced‘ only learned how to solve a case, but failed to do it in an organic and personal way.

Overprepared is telling the MD you've got a contact ready to send a shipment of 5 tonnes of marble slab to the Jersey City port because the foundation to his/her granite Roman statue in front of his/her estate in Westport (Connecticut) is discolouring.

That's overprepared, "done good research", "know the people", but way, way too creepy.

You want to be prepared in the sense that you have the technical understanding to tackle a question after a moment of thought and provide a fluid and natural sounding response that both answers the question and displays that you're not a robot. Being over-prepared comes off as disingenuous and scripted, which obviously is off-putting to an interviewer.

I agree with everything that was said in regards to canned frameworks, but you can also be over-prepared from an emotional perspective. There is a certain level of genuine excitement and enthusiasm that people bring early on in case practice that they tend to lose during later cases. That is not to say that you can't do 100 cases and come off as engaged and interested, but it is definitely something to be cognizant of.

Imagine you’re an explorer that needs to go into unfamiliar territory to accomplish some objective. Being over prepared means preparing the exact sequence of steps that you will take in this territory. Being effectively prepared means understanding the terrain that you should expect and having the right tools at your disposal, in order to successfully navigate through the territory and deal with unexpected obstacles that you might find on your journey

**TL;DR Interviewers are trying to learn about you and assess you for the role. If you are too prepared, they won't learn anything about you beyond the fact that you can memorize. In a competitive environment, that is not to enough. **

I think it is important to call out why being over-prepared is bad in the context of an interview.

The purpose of an interview, generally, is for the interviewer to gain information about the candidate and their skills to assist in determining if the candidate should be hired. So, when a candidate is too prepared, or at least appears so, the interviewer is going to come away feeling like the only information they learned was the candidate can memorize, which I am fairly certain is not the skill the interviewer is looking for. Sure the candidate may also possess those skills, but the interviewer won't know for sure. For a competitive position with a ton of competitive applicants, like management consultant, there is no reason for the company to take a chance when other candidates will have certainly shown more.

From my personal experience (not management consulting), one applicant I interviewed over the phone really stands out. His application and academic achievement showed he was clearly brilliant and hard-working, but lacked on-point experience. While I only saw the resumes of the people I interviewed, I would be flabbergasted if he did not have the highest intellect/IQ of any applicant for that position. However, it was unclear if he had the other skills needed to succeed in the role. The call started off with some nice small small talk and he was decently charismatic. Once the interview started, it was like a switch flipped. Every answer he gave, in a vacuum, would be objectively "very good," but was very clearly memorized. Every one, the exact same tone, cadence, and a level generality completely agnostic to role, industry, or interviewer. Even when I threw what I thought were curve balls, he had an answer ready just generic enough to answer the question without providing any real insight into anything. It was to the point I would not buy he just used a soundboard of recorded answers (no, I don't actually thing he did). I actually pushed for him to move on, probably because I'm a gambler, but with 100s of applications, the candidates who moved on (I was not the decision maker) were ones where there resume and/or interviewer could say they had what we were looking for. To this day I have no idea how he would have done in the role, and that was the problem.

Don't memorize the case prep; read the cases, use them to create a basic framework (your own, in your own words) and then apply that framework on the fly. If you focus too much on memorizing you will spend way too much time trying to recall it and it's one thing trying to do that while you're writing, but quite another during Q&A or a verbal case.