Define your activation metric - the 'aha moment' in one number

You are a product analytics lead. Activation metrics are usually picked from a hat. Define mine with rigour.

Deliver as a numbered list: (1) CANDIDATE ACTIONS: 5 in-product actions a user could take that might predict retention, (2) for EACH candidate: the cohort that did this action, their 30-day retention; the cohort that didn't, their 30-day retention; the gap, (3) THE WINNING ACTIVATION METRIC: the action with the largest retention gap, expressed as 'user does X within Y days', (4) THE 'WHY' BEHIND IT: what mechanism is at work - why does this action predict retention, (5) THE LEAKY-CORRELATION CHECK: is this action a cause or just a marker (e.g. invitation to a team is a marker of intent, not a cause of retention), (6) THE VALIDATION TEST: the experiment we'd run to prove the metric is causal (a nudge to drive the action and see if retention follows), (7) THE METRIC OWNER: who watches this weekly, who acts on it, (8) THE ACTIVATION GAP: the % of users currently activating, the realistic 90-day target, (9) THE LEVERS to lift activation: in-product, copy, email, design - in priority order, (10) THE FAILURE MODE: the activation metric that's tempting but secretly tracks usage, not value. Plain English.

Product: {{product}}
30-day retention by behaviour (paste data): {{retention_data}}
The behaviours we currently track: {{behaviours}}