The Two Most Important Tools...
"...an architect has are the eraser in the drawing room and the sledgehammer on the construction site."
--Frank Lloyd Wright
Guess which one is cheaper?
A key point is build twice--the first time on paper. Changes late in the game get you twenty to fifty cents on the dollar in terms of value, not to mention the cost of the do-over.
This is why iterating finish schedules are so important.
You start to understand materials in terms of thickness and edge conditions. Good interiors derive from so-so interiors. Mock-ups impact momentum a lot less than full scale model iteration. Sometimes your best design is a clever take on working within the project's constraints.
Remember the carpenter's maxim: "measure twice, cut once."