From our experience bad Anaplan model design results from limited understanding of mutually exclusive and collectively exhaustive data structures...

Mutual exclusive is a term applied to the grouping of data items whereby there is zero overlap between groups. Items belong exclusively to a single group. Collectively exhaustive is when all possible items are accounted for in our classification in the relevant combination, group or association. Why is mutually exclusive and collectively exhaustive (MECE) import to model design?