A central tenet of analytical problem solving is your considering all the possible solutions to your problem exactly once; that is, your approach must be mutually exclusive and collectively exhaustive (sometimes written as “mutually exclusive and completely exhaustive”)—or MECE (pronounced “me see”).
MECE thinking is very popular with strategy consultancies, including the McKinsey, Bain, and BCG of the world. In fact the case interview that these companies filter their applicants with are designed to test whether you can think in a MECE-way. It is understandable: MECE thinking is both efficient and elegant; so let’s look at what it means and how you become an effective MECE thinker.
Mutually exclusive means “no overlaps”
Two sets of elements are mutually exclusive when they don’t intersect: you cannot have an element belonging to both sets at the same time.
When you are mutually exclusive in your approach, you consider each potential solution only once, hereby ensuring that you do not duplicate efforts. (In the tile roof of the image above, that means that you don’t have several tiles stacked up to cover the same spot.)
Mutually exclusive thinking forces you to consider the details, seeing the individual tree as opposed to the forest. It helps you ensure that each element is different than the others.
So if your key question is “How can I go from New York City to London?” and you reply by first dividing means of transportation between “flying” and “traveling by sea”, you are organizing the possible solutions to your problem in a mutually exclusive way (since if you’re flying you are not traveling by sea at the same time).
Collectively exhaustive means “no gap”
Groups of solutions are collectively exhaustive when, in between them, they include all the possible answers to your problem.
When your analysis is collectively exhaustive, it includes all possible solutions at least once. (In the tile roof of the image above, that means that you’ve covered the entire area, with one or several layers of tiles, leaving no gaps.)
Collectively exhaustive thinking helps you ensure that you do not forget possible solutions; that is, you must be innovative, viewing the forest as opposed to its individual trees.
Thinking in a collectively exhaustive fashion when you’re considering ways of going from NYC to London means that by considering air- and sea-transportation, you have found a complete set of answers to your problem (since there are no land connections between the US and the UK, so you cannot travel by land, and teletransportation still doesn’t exist).
Being MECE will drastically improve your thinking.
MECE thinking is perhaps the most important concept in analytical problem solving. The concept is simple to understand but it can be challenging to apply in some fields. That’s because we’re usually better at either considering minute details or the big picture but not both, let alone at the same time. Becoming a strong MECE thinker takes training and you should make it a habit to think in MECE ways.
Making it a habit means that, each time you are confronting a new problem, you need to actively look for a MECE way to break it down in its root causes and/or solve it. All your issues trees have to be MECE.
In day-to-day life, you can also train yourself to be better at thinking in a mutually exclusive and collectively exhaustive way: each time you’re looking at a series of items, ask yourself if they are MECE. Whenever you see or hear a list of things—listening to the latest tirade of your favorite politician or the verbose argument of a close friend—ask yourself if it is indeed MECE. Become obsessive about it. If you start waking up in the middle of the night yelling “This is not MECE!”, then you’re on the right track…