There are a great many exceptions; too many to list - think just of the inventions that have been lost for centuries or millenia. Forceps were the trade secret

There are a great many exceptions; too many to list - think just of the inventions that have been lost for centuries or millenia. Forceps were the trade secret of one family of doctors for many generations. The Chinese invented stainless steel, the Romans succumbed to armies equipped with it in the east but never discovered how to make it. Mendel. Etc, etc. Some discoveries, once overlooked, can be overlooked for a very long time. But this may reinforce the author's point - new fields don't stay new, everyone's attention moves on and the chance for easy discovery may be lost. We would be wise to invest heavily in trying to discover what we've overlooked.