alt Hacker NewsI know a guy who's done systems work for 30 years. He's good at getting promoted; goes around "getting things done" and leaves a huge mess. Hasn't learned anything new, just knows enough to be dangerous. Wouldn't pass a test for a role his title indicates. But he'll get hired for it today, based on a resume.
No formal testing means no formal education which means a lack of important detail. You know how you learn the details on the job? By screwing up the job. You gonna let Eddie The Trainee Surgeon work on your brain after leaving a medical school with no grades?
It's called residency. They work as trainees and build up the initial experience under someone.