CI failures have a reputation for being cryptic. After years of staring at GitHub Actions logs, I've found that 90% of all failures fall into one of five categories. If you know the categories, you can diagnose any failure in under 10 minutes.
Step 1: Read the Full Log
GitHub Actions collapses log sections by default. Always expand the failing step and scroll to the first error, not the last. PHP and Laravel produce cascading errors — one root cause produces 50 error lines. The one that matters is always at the top.
The Five Failure Classes
Class 1: Missing File or Directory
