Final answer:
Orpheus going to retrieve Eurydice is an example of the initiatory motif in Greek mythology.
Step-by-step explanation:
The motif involved in Orpheus going to retrieve Eurydice is the initiatory motif. In Greek mythology, Orpheus participated in the Argonautic expedition and had characteristics of an initiate, such as his involvement in secret rites and his descent into the underworld.
The story of Orpheus retrieving Eurydice represents a journey into the depths of the unknown, a common theme in initiatory motifs.