Debugging Systematically

Debugging systematically

Don't guess-and-check by editing code and hoping. Work the actual chain of evidence:

1. Reproduce it. Run the exact failing command/action before touching anything — confirm the same failure, not a different one.
2. Read the real error, not the symptom. A stack trace or exit code tells you where, not always why — but it's still the starting point.
3. Narrow the cause. Check logs (shell to tail/grep them), add a temporary print/log if the failure point isn't obvious, or bisect (isolate half the suspect code) rather than reading the whole codebase hoping to spot it.
4. Form a specific hypothesis before changing code — "X is null because Y never sets it," not "let me try changing this and see."
5. Fix the root cause, not the symptom — a null check that hides a bug is worse than fixing why it's null, unless null is actually a valid, expected state.
6. Verify the fix by re-running the exact repro from step 1, not just "it looks right now."

If a fix doesn't hold up on verification, don't layer another patch on top — go back to step 3. Two unexplained fixes stacked on each other usually means the real cause hasn't been found yet.