Structural analysis is a mode of analysis that posits a binary symmetry that whenever in a given version of a myth or a detail appears as a bit 'off pattern', it is most likely trying to say the opposite of a different version which exist elsewhere and usually not far from the other one.
Structural analysis is necessary because society, any society, is concerned immediately to structure reality.
Structural analysis is grounded in the idea that whenever a detail seems a bit 'off pattern' in a version, it is likely that it is expressing the opposite of a normal version which exist elsewhere and usually not far from the other one.