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 (see, for instance, Davis et al. and Kazancioglu et al., referenced below). In fact, the case interview that these companies use to filter their applicants require you to think in a MECE way. It is understandable: MECE thinking is efficient and comprehensive; so let’s look at what it means and how you can become an effective MECE thinker.
Mutually exclusive means “no overlaps”
Two (or more) 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 thinking, 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 differs from the others.
So if your key question is “How can I go from New York City to London?” and you organize means of transportation by dividing them between “flying” and “traveling by sea”, you are organizing the possible solutions to your problem in a mutually exclusive groups (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 means 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).
MECE thinking is arguably one of the most important concept in analytical problem solving. While simple the concept can be challenging to apply in some situations. One reason is because we’re usually better at either considering minute details or the big picture but not both, let alone at the same time. Another reason is the nature of the problem itself: a profitability problem is easily broken into revenues and costs—two neatly MECE components—but if your problem calls for, say, defining types of intelligence, finding MECE groups may be challenging (Harvard’s Howard Gardner has a proposal, though). Becoming a strong MECE thinker takes practice, and you should make it a habit to think in MECE ways.
So, each time you are confronting a new problem, actively look for a MECE way to categorize its root causes or its solutions, and ensure that all your issues trees are 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…
Use help wherever you can
Sometimes, you’ll be lucky enough to have existing frameworks that you can use to decompose your issue in MECE parts. If one of these is insightful enough for your situation, use it.
If you’re not that lucky, you’ll have to come up with your own MECE set. That can be tedious. Then it may be a good idea to enlist others to question your logic and help you push yourself.
Learn more about thinking MECE
MECE thinking also has limitations; here is more on that.
Davis, Ian, David Keeling, Paul Schreier and Ashley Williams. “The Mckinsey Approach to Problem Solving.” McKinsey Staff Paper, no. 66 (2007): 27.
Eppler, Martin J. “Toward a Pragmatic Taxonomy of Knowledge Maps: Classification Principles, Sample Typologies, and Application Examples.” In Information Visualization, 2006. IV 2006. Tenth International Conference on, 195-204: IEEE, 2006.
Gardner, Howard. Frames of mind: The theory of multiple intelligences. Basic books, 1985.
Kazancioglu, Emre, Ken Platts and Pete Caldwell. “Visualization and Visual Modelling for Strategic Analysis and Problem-Solving.” In Information Visualisation, 2005. Proceedings. Ninth International Conference on, 61-69: IEEE, 2005.