I think that when you see enough of it, these things are pattern matched idioms in your head. You hardly even consciously think about it. You have x, you y and you need it transformed to z; you did something like that 1000 times before and because the language is so terse, you remember the snippets of incantations to do it without looking anything up.

When I programmed Pascal decades ago, I had my own lib, which was huge, it was just a massive collection of functions pulled from projects which I all wrote myself and all remembered (and still remember). When I had to build something, it was mostly cobbling together those functions. Worked a lot faster (with more stable results) than Google->SO or npm search and install.

APL(/j/k) have that but with the added benefit that you don’t have to write or download a library; everything is composable, so instead of remembering/searching the functions I (or someone else wrote) remember the actual implementation... Which, in those languages, is usually the same amount of chars as the function name and usually smaller than the function name with params.