> The **MECE Principle** is a grouping principle for separating a set of items into subsets that are mutually exclusive (ME) and collectively exhaustive (CE). **Mutually Exclusive**: Two events are ME if they can't both occur at the same time. **Collectively Exhaustive**: A set of events is CE if at least one event must occur. MECE is commonly used to break down complicated problems into smaller problems which can be solved separately, and combined together. MECE may not be sufficient for understanding complex problems, where the whole system behaves differently from the sum of its parts.