Q: A developer pushes code that passes all unit tests and builds successfully in CI, but when it deploys to production, the application crashes immediately. Why might this happen?

This is the classic "It works on my machine" problem scaled to production. The most common causes are:

• Configuration Mismatch: The production environment relies on environment variables, secrets, or database URLs that are either missing, misspelled, or configured for the staging environment (e.g., trying to write to a staging DB with production locked-down credentials).
• Dependency Drift: The CI pipeline might be downloading the "latest" version of a transitive dependency (npm, pip, maven) which introduced a breaking change not captured in the developer's local package-lock or requirements.txt.
• Infrastructure Differences: The code might have an implicit assumption about the underlying OS (e.g., specific file paths, package versions) that differs between the local/CI environment and production.