History is full of great ideas that did not succeed — frequently because they did not meet the “needs” of the marketplace. One of the first things I learned as a fledgling product designer is that you won’t have a successful project if the mission keeps changing. Whether you call it a scope of work, a product specification, or a requirement list, you need an accurate “target” to aim at.
Think about that classic Mad Magazine cartoon of the King shooting an arrow at a blank target and the loyal minions dutifully drawing a bulls-eye around it.
You are not that king!
Your customer rules and it is not unreasonable to expect them to fully describe what they want you to build. Sales people are notorious for “mission creep” and do not like to be reminded of it; trying to hit a moving target greatly reduces your chances of success.
So what is in a “good” product specification? It can be as simple as an outline drawing that defines the interface points and lists the expectations on rotation directions, shaft speeds, and power capacity. There are great checklists in some catalogs. API has a multi-page form; AGMA 6006 has an appendix on what is needed to properly specify a wind turbine gearbox.
Far more difficult is the complex definition of a new product line. Millions of dollars can be spent on research, focus groups, and math modeling — only to completely miss what the ever-fickle marketplace wants. Think “Edsel” versus “Mustang.” Same company; probably some of the same people, yet the results were vastly different. One project almost instantly became synonymous with failure; the other defined a sub-market that endures 63 years later.
It is pretty easy to say “Be the Mustang” in your market, but very difficult to pull off. Most of the individual parts in that legendary design were borrowed from the successful but easily forgotten Falcon. The bits do not matter if the overall package is not appealing, so the specification has to be more than just a checklist.