Research and development is a very professional sounding term for the process of making mistakes.
We make prototypes because we understand that ideas do not always come complete and there are some (or many) details to be worked out.
In a production environment, R&D usually leads to a final design that is then produced over and over. The production is a fixed process and the outcome is predictable. But in a custom shop, the paradigm is a bit different.
I have always done one-off projects. The customer does not want a door design that umpteen other people already have. They want something unique, something that they can look at and think, "I'm the only one who has this."
In situations like this R&D is often done "on the fly". You have to make it up as you go. This is a risky process because any mistakes are going to come out of the profit on that project. Many is the time I woke up with the realization that what I was planning was not going to work. Then it's stress time as I tried to work out an alternate method that would result in the same appearance I had already sold the customer on.
Over the years, the process is repeated and results, hopefully, in what we call experience. You get to where you can see more of the pitfalls up front and understand how to avoid them. Sometimes, but not always.