> I think what they meant is you “can save 10 hours of planning with one hour of doing”

I know what they meant, and I also meant the thing I said instead. I have seen many, many people forge ahead on work that could have been saved by a bit more planning. Not overplanning, but doing a reasonable amount of planning.

Figuring out where the line is between planning and "just start trying some experiments" is a matter of experience.