I’ll agree or argue, depending on your perspective, that it’s not always best for a project to turn out exactly as planned.
The Wright brothers had, as a guiding principal, "Get it right on paper first." The problem is that, when it comes to design, what looks great on paper might not look all that good in 3D. There are so many subtleties in line, form, balance and proportion, any of which can make or break a design.
Sam Maloof used to talk about the ‘hard line’ he used so effectively in his furniture. "Making the hard line is easy," he would say. "But making it mean something is the key."