Understanding something’s affordances is isomorphic to being able to go up and down the The ladder of abstraction with the thing because you both need to see the possibilities for using the thing in a completely different context (at the top of the ladder) but also understand how and why it would work in that other context which requires being at the bottom of the ladder.
Once you understand the affordances of a thing, you can take action with confidence. Legibility enables action.
Because understanding requires intuiting affordances, for most people Staying at the top of the ladder of abstraction is mystifying.
Something about understanding the assumptions