The 100 meters is the most unfair race in track and field.
One tiny mistake can cause a runner to lose a second (often 1/10 of a second) and miss a medal after years of intensive training.
Can you imagine Akani Simbine lying in his bed and thinking over and over about his race and why he missed a medal by a ridiculous 0.04 seconds?
Probably he was haunted by this race for weeks, if not months.
Case interviews are like that.
Hard.
Unfair.
Because a single mistake can destroy your chance to join your dream top-tier consulting firm.
That’s why today, we will talk about a few fundamental case interview mistakes that I’ve seen candidates repeatedly dinged on.
More precisely, this article is about the 16 most common case interview mistakes.
Table of Contents
Case interview mistake #1 lowering your chance of landing a job offer: solving the wrong problem
Asking the right clarifying questions in a case interview is essential to start the case interview on the right track.
You need to ask the right clarifying questions to understand the case context and objective.
The last thing you want to do is to discuss the wrong problem with your interviewer for 20 minutes.
Here is an article to start your case interviews on the right foot.
Now let’s move to the second of the 16 most common case interview mistakes.
Case interview mistake #2 lowering your chance of landing a job offer: building an incomplete issue tree
This mistake is the worst on this list.
I can almost hear candidates saying, “But I used a framework!”.
Yet, the failure here is twofold:
Firstly, the candidate will often not lay out a structured and logical approach to how they would think about solving the case.
There is either no structure, a generic framework, or just a laundry list of things they would think about, often only focusing on one or two areas and going way too deep right off the bat.
And yes, most frameworks you can find in well-known books are generic and not MECE.
A good structure lays out a broad approach that covers all the key issues and can be used to solve the problem efficiently.
Second, there is no clear structure to the candidates’ thought processes.
Interviewers seek clear evidence that the candidate follows a logic-driven, structured thought process in each part of the case problem.
You can learn frameworks, but structured thinking is a much harder skill or mindset to fake.
Here is an article to learn more about the MECE principle.
Case interview mistake #3 lowering your chance of landing a job offer: boiling the ocean
In consulting, ‘boiling the ocean’ means doing analyses without a particular purpose.
It’s like looking for something somewhere: this is inefficient and a waste of time.
And obviously, consultants want to solve their clients’ problems as fast as possible (time is money).
Candidates who randomly ask for data without explaining their thought processes are rejected.
Instead:
Use a hypothesis-driven approach where the end goal and the necessary analyses to reach this goal are clearly defined.
Now let’s move to the fourth of the 16 most common case interview mistakes.
Case interview mistake #4 lowering your chance of landing a job offer: don't communicate your thinking process
Since interviewers use case studies to understand your thinking, guiding the interviewer through your thinking process is extremely important.
Even if you provide a solid answer in the interview, you will likely be successful if the interviewer understands how you arrived at that answer.
Therefore:
Tell the interviewer what you think, and explain your plan for solving the problem.
Interviewers want to understand your logic and way of thinking, not to get a “correct answer”, which does not exist.
Case interview mistake #5 lowering your chance of landing a job offer: spending too much time on irrelevant issues
You know this: time is money.
This statement is particularly true in consulting.
Consultants are obsessed with the Pareto rule: doing the 20% of analyses that will solve 80% of the problem.
And your case interviews mimic real-life consulting projects:
You have little time to solve a complex problem.
And your interviewers will assess your ability to prioritize the issues that require further analysis (and those that don’t need to be analyzed).
So, prioritize case discussions on issues that maximize customer value, and you’ll avoid this common cause of rejection “you spent too much time on irrelevant issues.”.
Case interview mistake #6 lowering your chance of landing a job offer: not being able to progress without help
If an interviewer needs to constantly prompt the candidate on what they would do next, the possible solutions, or the broader implications, then those candidates are failing.
Think about this:
Consultants are hired to take the initiative and solve problems.
And Managers (in Consulting) want to avoid being constantly bugged with ‘I have done X, what do I do next?
Now let’s move to the 7th of the 16 most common case interview mistakes.
Case interview mistake #7 lowering your chance of landing a job offer: losing sight of the big picture
Instead of treating each question asked by the interviewer separately, you want to connect the dots and bring it back to how each question contributes to solving the central problem.
It always helps to tell your interviewer at each step of small conclusions how they lead to or avert the next steps of the process.
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Case interview mistake #8 lowering your chance of landing a job offer: lacking creativity
Your interviewer has likely done a lot of case interviews and has potentially given the same case a dozen times.
If a candidate comes up with a creative, practical, and new answer that the interviewer has never heard, they will almost fall off their chair and award big bonus points.
The alternative is the candidate that rolls out a generic approach, identifies the standard answers, and makes a safe recommendation.
The failing here is not giving the interviewer reason to push for you; remember that MBB wants star candidates to join their ranks of super intelligent and engaging employees.
You must show that you fit that mold (hopefully in a diverse way!).
Getting a ‘they were ok….. maybe’ is a fast track to rejection.
Case interview mistake #9 lowering your chance of landing a job offer: making calculation mistakes
All interview cases include some math.
Usually, you’ll have to compute very elementary calculations using the four basic operations (addition, subtraction, multiplication, and division).
Many times, candidates asked me if they could use a calculator.
And unfortunately, the answer was and still is no!
Being able to do mental calculations quickly is essential not only during interviews but sometimes also during real project cases when I have to assess on the spot during client discussion the potential quantitative implications of some decisions and give my opinion about them.
Now let’s move to the 10th of the 16 most common case interview mistakes.
Case interview mistake #10 lowering your chance of landing a job offer: not interpreting data
The math performed during a consulting case interview is never there just for doing math.
Conversely, calculations are part of a larger business problem you need to solve.
And in my experience, many candidates get drawn into calculations and arrive at the correct final number but forget why they were doing the calculation and the real purpose of the number they just discovered.
Case interview mistake #11 lowering your chance of landing a job offer: not sense-checking calculations
Math mistakes are entirely acceptable (for most interviewers, not for all).
However, what is not tolerable is not being able to catch your error, even though the answer you got makes absolutely no sense in the context of the case.
If that happens, you have added poor judgment to your miscalculation.
An example of this mistake comes from a candidate who told me that according to his calculation, the average salary of a blue-collar in Germany was close to 10 M$ per year.
This candidate not only screwed up his calculation (which is acceptable for most interviewers) but also completely lacked common sense in his answer (that is much worse).
Case interview mistake #12 lowering your chance of landing a job offer: communicating ideas in an unstructured manner
Clear communication of your approach and tactics is crucial to case interviews.
As a Consultant, you’ll be dealing with senior executives who won’t have the time to go through every detail.
That’s why:
You always want to start with the key message.
Then, you move to your supporting arguments to explain why your key message makes sense.
This approach is also called the Pyramid Principle. It’s core to how consultants communicate.
It was first introduced by Barbara Minto in the 1970s and became widely used in the industry.
Case interview mistake #13 lowering your chance of landing a job offer: not being concise and sharp
A recommendation – at the end of a case interview – is like bumping into your client’s CEO and telling them where the case is.
A great candidate will clearly state the answer to the case and then give a crisp synthesis of 3-5 reasons why.
The trap some candidates get into is just walking through a list of everything that they looked at.
A great candidate will also include the following steps or uncertainties.
Case interview mistake #14 lowering your chance of landing a job offer: showing poor enthusiasm and low confidence
Interviewers are looking for candidates who are client ready.
Which means:
If they took them to a client meeting with a client, they would reflect well on the firm.
Therefore, great candidates can project confidence and come across as considered or thoughtful.
It’s ok to be nervous.
And most interviewers allow for it and will help settle your nerves.
Dress smartly, sit up, talk slowly, pause and think before speaking, and don’t ramble!
Case interview mistake #15 lowering your chance of landing a job offer: not following interviewers' guidance
It is also important to be coachable, which means listening and responding to feedback from the interviewer in the form of verbal or visual cues.
However, this does not mean you shouldn’t appropriately defend your position.
But interviewers want to help you out, and if you are pushy or not receptive, then you are not someone they would want on their team.
Now it’s time to talk about the last of the 16 most common case interview mistakes.
Case interview mistake #16 lowering your chance of landing a job offer: showing poor business acumen
This does not mean business knowledge, so non-commerce applicants don’t despair.
Business Judgement is about sense-checking answers and thinking through the broader implications, such as implementing recommendations.
You can imagine a whole shopping list of ways to fail this one.
Proposing an utterly impractical solution, not considering the broader implications of an option, claiming to be able to deliver 40% cost savings in 1 year, and planning for 50% market share in a highly competitive and fragmented market, etc.
The list can go on and on!
The key is that answers need to be vetted, wider implications (people/risks, etc.) thought through, and knowledge and appreciation of the current business world and market demonstrated.
Conclusion
This article listed the 16 most common case interview mistakes.
For many people, walking out of a job interview thinking they have done a ‘good’ job will be enough for success.
Unfortunately, in the world of management consulting and case interviews, good isn’t quite enough to cut it.
Applicants receive calls telling them they have been unsuccessful because they have been good but not great.
Given that MBB and other consulting firms are after the ‘best of the best’ it is not surprising that only being good isn’t enough.
Thus, avoid all the above mistakes and you will be among the top 1% of candidates.
Now, leave a comment below to tell me with what you are struggling the most.
Sébastien
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You need 4 skills to be successful in all case interviews: Case Structuring, Case Leadership, Case Analytics, and Communication. Join this free training and learn how to ace ANY case questions.
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