This poem by W. H. Auden captures the essence of the expert. Is there a skill, that when you do it, someone doesn't need to look at what you're doing but rather at the look in your eye, your attention to detail, and the passion in your commitment?
You need not see what someone is doing
to know if it is his vocation,
you have only to watch his eyes:
a cook mixing a sauce, a surgeon
making a primary incision,
a clerk completing a bill of lading,
wear the same rapt expression,
forgetting themselves in a function.
How beautiful it is,
that eye-on-the-object look.