MECE
No overlaps. No gaps.
An overlap funds two projects for one problem. A gap leaves you fixing the half you could see.
Mutually exclusive
One item, one bucket. Nothing gets counted twice.
Collectively exhaustive
Every item has a bucket. Nothing gets missed.
The same question, cut twice
Five engineers planned six weeks. It took ten: twenty dev-days of work nobody planned, and a week that kept shrinking.
What the retro said
The two checks
Overlaps
one pairSlow review and too many meetings are the same queue of hours, counted twice.
Gaps
15 of 20 daysItem 02 covers five of the twenty days the job grew. Item 03 names the holidays, not the interview loop.
Where the list came from
Round the room, one item each. Things people noticed, not causes.
Two branches, then their parts
A The job got bigger +20 days
A1 Scope added after kickoff 9 days
A2 Work we found on the way 6 days
A3 Rework on finished items 5 days
B The week got smaller −6 a week
B1 Fewer people available 3 a week
B2 Hours going elsewhere 2 a week
B3 Blocked waiting on others 1 a week
The two checks
Overlaps
noneEvery dev-day lands in one term or the other, never both.
Gaps
noneNothing moves the date without moving one of the two terms.
Where the cut came from
Fix only the scope and it still takes 8.6 weeks. Fix only the throughput, seven.
MECE is a test, not a goal: a cut can pass both checks and still land where nobody can act. Cut where the actions differ, then check, because an Other bucket buys exhaustiveness and says nothing.
Every item in that retro was true. Fifteen of the twenty days were not on the list.