Why it matters
Acquisition is expensive; churn silently cancels it. A business winning ten clients a quarter while losing eight is running hard to stand still, and the fix (why do they leave, and when?) is usually cheaper than more marketing. Retention is growth's quiet twin.
How it works
Count who was a customer at the start of a period and who remained at the end; the leavers over the base is your churn rate. The insight lives in the pattern: when in the lifecycle people leave, which segments leave most, and what the leavers had in common.
What to do about it
Measure it properly (including the "quiet" churn of clients who just fade) and interview five recent leavers. Their answers are the highest-ROI research most businesses never do.
