Pull the Thread

Definitions

To follow one clue or inconsistency deeply enough that it starts unraveling the larger situation. In engineering slang, pulling the thread is how minor weirdness sometimes reveals the whole hidden structure underneath.
In plain English: To investigate one clue until it unravels the bigger problem.
Example: "They pulled the thread on one duplicate event and ended up uncovering an entire class of idempotency failures the dashboards had been masking."