Mechanics hear a problem before they see it. Experts are just people who paid attention for years.

Expertise sounds like intuition and is mostly accumulated noticing. Somebody who has heard ten thousand engines has a library to compare this one against, which is why the diagnosis arrives before the inspection and looks like a gift. Nobody handed them that. They were paying attention while everyone else heard noise.

Pick one thing you want to get good at and start noticing details in it on purpose, not just doing it. Keep a short note of what you observed each week. The library builds faster than you would think.