Final answer:
The statement 'D) Daoism originated in a single, clearly defined historical moment.' is not a legitimate reason for the difficulty in pinpointing the origins of Daoism because Daoism emerged over time with various influences and multiple roots.
Step-by-step explanation:
The statement that does NOT reflect a legitimate reason as to why the origins of Daoism are hard to pinpoint is: D) Daoism originated in a single, clearly defined historical moment. This statement is incorrect because Daoism is known to have emerged gradually over a long period of time, influenced by various ideological systems, and without a single, clear-cut origin. The other statements accurately reflect the complex and multifaceted development of Daoism across different historical periods and through a variety of influences. Historically, Daoism has been open to a range of interpretations due to the elusive nature of the dao, which suggests an underlying natural order to the universe that's inherently open to individual interpretation.