The professional engineer has indeed endured certain rites of passage--proofs to his peers that he can function in the required capacity. No one said anything about error-free calculations, only a reasonable standard of care.
I maintain that the main concern of the engineer is economics and not technology. Technology is important, but it is secondary to economics. The three elements of a project--scope, schedule, budget--are all economic considerations that the engineer must make decisions about. Engineering something out of a catalog is no different. No engineering project ever got shot down only because it was technically not do-able, but projects die everyday for lack of funding.
I also belive that most engineers desire the technology to be foremost, which accounts for the typical engineer's continual frustration with management (a la Dilbert). Management understands the primacy of economics. Someone wrote in a related forum that at some point you have to shoot the engineer and start production. Hey, I are one, so I understand.
Someone who is continually going back to first principles, and who lacks one or more of the above listed constraints, especially scope, is a scientist, not an engineer. However, even a scientist will begin by studying the relevant literature to find out what has gone before.
I suppose that I am distinguishing between engineering for revenue generation and engineering for invention or R&D. I am a consultant whose clients don't want brilliant innovations; they want tried-and-true technologies for a given scope, schedule, and budget. There are engineers developing those technologies, but even they rely on previous engineering to put a system together, standing on the backs of giants, as it were.
Cordially,
William