Experts look like they do it wrong
Flyvbjerg 2001. Had videos on paramedics doing CPR, some of them beginners (i.e. had just finished their training), and some of them experienced. When you show these videos to experienced paramedics, they can guess correctly that the person in the video was experienced (90% correct rate), whereas if you show them to beginners, they're just guessing (50-50 correctness rate). The interesting part is when you show the videos to teachers of paramedics. These did worse than guessing, systematically mistaking the experts for beginners and beginners for experts. This is because beginners go by-the-book, exactly the methodology the teachers taught, and the experts know when to diverge from the book, which looks like doing it wrong.
Hubert and Stuart Dreyfus have a five-grade expert scale, and completed training puts you on grade 3, a "performer", and many teachers cannot detect where you are beyond grade 3.