Systematic Debugging

Guessing wastes time and ships new bugs. The first explanation that comes to mind is usually the symptom, not the cause. This skill is the investigation discipline you run before you are allowed to touch a fix.

The one rule

No fix until you have found the root cause. Finding the cause is a separate step from fixing it, and it comes first.

If you have not finished Phase 1, you do not get to propose a fix. Not "probably", not "let me just try", not "this should do it". Find the cause, then go to [[fix]] to fix it properly.

Run this even when — especially when — the bug looks trivial, you are in a hurry, or someone wants it fixed now. Simple bugs have root causes too, and systematic is faster than thrashing through five guesses.

Phase 1 — Find the root cause

Before changing a single line: