If it quacks like a duck - it must be a duck. Not really.

> In every profession there’s a point where further improvements in skills are so subtle that the difference between one level and another can only be appreciated by another expert

Goal defines the benchmark for proficiency.

Better tennis player scores. Better software engineer writes more space/time efficient code or solves business problem faster (whichever the objective). Better writer gets more views or inbound sales or whatever the goal is.

If you get better at achieving ever greater goals, then your expertise is growing. No amount of luck can compensate for a lack of expertise.