Mistake
What happens
Do this instead
Assume a metric is valid
Release gates built on SQL correctness. After launch, abandon rate climbs from 12% to 25%.
Correlate it with a lagging metric before it gates anything.
Optimize a proxy
Latency drops from 150ms to 80ms. Satisfaction stays flat.
Name the user behavior that should change first.
Test set drifts from production
95% quality on the test set, 70% satisfaction from real users.
Compare offline and online scores. Rebalance the test set.
Let a proxy go stale
A gate validated in Q1 is still gating in Q3 after users' priorities moved.
Recompute each correlation quarterly.
Mix up the layers
Waiting two weeks on satisfaction surveys to judge each change.
Iterate on leading metrics. Validate on lagging ones.