Part 8 · 1 chapters · ~8 min
Case Drills
Practice problems across software, operations and product, each with the move it rewards and a worked outline: a slow page, a duplicate payment, a flaky test suite, a stalled migration, a support backlog, and a launch with falling conversion.
15
Six drills
| drill | the move it rewards | outline of a good answer |
|---|---|---|
| a statement page takes 9 s for some users | scope first | which users? (large accounts) → which part? (query) → known problem? (missing index, offset pagination) → fix and verify |
| a customer was charged twice | understand before fixing | confirm with the ledger, find the path (retry without idempotency key), refund, then fix the class of bug |
| the test suite fails randomly 15% of runs | measure and decompose | record failures per test, find the few flakiest, categorise causes (time, order, shared state), quarantine with owners |
| a migration stuck at 80% for two months | unblocking | list remaining users, owners and blockers, do the last ones yourself, set a removal date |
| support backlog doubling | systems thinking | stock and flows: which inflow grew? fix the source, not the queue |
| a launch where conversion fell | statistical thinking | check segment mix and instrumentation before blaming the feature (Thinking P4) |
Practise by writing an answer in ten minutes, then comparing with the outline: the goal is to recognise which move each situation calls for, quickly.