Writing.
Visible skills: being able to get your point across exactly they way you want to, proper word-choice where nuance can change the entire meaning of a sentence etc.
Invisible: understanding the "melody" of text. It's a bit hard to explain. Good text flows according to your personal rhythm.
Cezary Jan Strusiewicz
I've been thinking a lot about visible vs invisible skill layers. i.e every craft has outer layers of skills that laypeople can recognise, and inner layers that you need expertise and experience to perceive at all. Could y'all think of examples of visible vs invisible skills in your own discipline?