Exceptional engineers...can debug anything, quickly. Not by guessing - they shun superstition[1]. Instead, guided by instinct, but with rigor and process, they will narrow in on the root cause from different angles. They've a wide arsenal of sources and techniques to gather information; from the code and tests, the network, the OS, the DB, and from logs and metrics. They won't stop till they've found the actual root cause.
— Darragh Curran, The Difference Between Good and Great Engineers
The linked article on programming via superstition is worth reading - it explains how developers often make changes without understanding why they work.