Systematic Debugging

This is the "stop guessing and find the root cause" skill for when you're tempted to just try fixes until something works. It enforces a four phase process: investigate the root cause first (add logging at component boundaries, trace data flow, read error messages completely), analyze patterns by comparing against working code, form a single testable hypothesis, then implement one fix with a failing test. The iron law is no fixes without investigation, even when you're in a hurry or the solution seems obvious. What I appreciate is the "three failed fixes" rule that forces you to question whether the architecture itself is wrong rather than attempting fix number four. It's opinionated about the fact that systematic debugging is actually faster than thrashing, even under time pressure.