While your favorite strategy consultant will brag about the importance of MECE thinking, mutual exclusiveness (ME) is not what you should aim for.
Instead, you should concentrate on independence (I).
When two events are mutually exclusive, choosing one precludes the other from happening. But this is not always desirable:
For example, if you are interested in improving the financial performance of a company, you can reduce costs or you can increase revenues.
But you can also do both: increasing revenues does not preclude you from reducing costs.
So these elements are not mutually exclusive in the strict sense.
Rather, they are independent: you can pursue one independently of the other.
Or you can pursue the two.
Independence is a necessary condition for mutual exclusiveness.
Sometimes, it just happens that your solutions are ME: when deciding how to travel from NYC to London only once, going by plane precludes you from going by, say, submarine.
In this case, your options are not only independent, they are also mutually exclusive.
But that’s more a characteristic of your problem than of your thinking pattern.
In short, you should focus on thinking in independent ways not in mutually exclusive ones.
Events are collectively exhaustive (CE) when, in between them, they include all the possible outcomes of a given situation.
So your analysis is CE when it includes all the possible answers.
Source, Arnaud Chevallier, Rice Univ,, Structured Problem Solving, unpublished manuscript