I dont think any complex plan should be planned in your head. But drawing diagrams, sketching components, listing pros and cons, 100%. Not jumping directly into coding might look more like jumping into spec writing a poc
Maintaining a 'mental RAM Cache' is a powerful tool to understanding the system as a whole on a deep and intuitive level, even if you can only 'render' sections at a time. The bigger it is the more you can keep track of to be able to foresee interactions between distant pieces.
It shouldn't be your only source of a plan as you'd likely wind up dropping something, but figuring out how to jiggle things around before getting it 'on paper' is something I've found helpful.
Following the RAM analogy, this sounds like saving files only in RAM, instead of creating the files in the file system, persisted on disk, and then caching it in RAM.
Personally, for me without writing or sketching I cannot think complex things: as in complex logic, constraints, etc.
I guess this is topic too abstract, so we can read into it different things.
I dont think any complex plan should be planned in your head. But drawing diagrams, sketching components, listing pros and cons, 100%. Not jumping directly into coding might look more like jumping into spec writing a poc