In my world there are four levels of expertise: beginner, basic, medium and expert.

When most people have left the “beginner” level, they think they‘re at “medium” level. They‘re not. They‘re at basic level.

There is an ordered progression upwards through these levels generally enabled by experience, not just study.

It’s also been (correctly) pointed out to me that experience is not a scalar quantity, and the time to move between levels is vastly different, increasing at probably something approaching an exponential rate as you go up levels.