An idea is the beginning of an invention; a prototype is the beginning of a product.
Prototypes are critical to success. Some inventors focus excessively on the initial idea and invention and too little on creating and refining prototypes.
The first prototype can be crude. It is more important to get started with prototyping than to attempt to create a finished product too soon. Each prototype teaches the inventor something of value that will help in shaping the next prototype.
Perhaps the first prototype will be too large. Very often, the first prototype is too gadgety or complicated and must be simplified. Simple is almost always better.
It is important to get several prototypes done prior to filing a patent. Otherwise a critical epiphany that could shape a better product may not be captured in the patent. Typically, the biggest design changes and refinements occur with the first several prototypes.
Sometimes the inventor can make prototypes herself. Sometimes she must find resources to help with prototypes. There are many resources, including university design departments, companies with 3D printers and others. An inventor must be just as creative in finding and using cost-effective resources as she is in conceiving and developing new inventions.
Good prototypes result in good products. Start working on prototypes early and work hard at the process and you will be rewarded.