Keeping MECE (Mutually Exclusive and Collectively Exhaustive) is one of the biggest challenges for applying the logical thinking concepts for practical issue-solving.
In my class, students learn how to develop a logic tree while keeping the MECE structure in a practical way.
One of the tips is using “Pair concept” for coming up with possible alternative ideas.
The concept logically leads to a solid logic tree as follows:
Once you have an idea of possible cause (in the chart above, “Promotion was not effective”), you may draw an alternative cause by asking yourself “WHAT IF this is not a cause”.
In the chart above, the alternative is “Price up”.
Similarly you may repeat the same practices until you cannot come up with any other ideas.
In addition to the simple “pair concept” practice, you may apply the “category approach” as follows:
The words in blue in the chart above show “category names”, while descriptions in the white boxes are possible causes.
Using “Category names” allows you to lead alternative ideas much more easily by applying the pair concept to the category itself, rather than to the possible causes.
In my problem solving class, students repeat this excercises until they can make a solid tree showing all possible causes logically. It does not take much time, only a couple of practices are required.