DISCLAIMER: This may not be the place for this, but I wanted to keep it out of off-topic.
So, we all know the stereotypical dream-anecdote in pre-modern biographies where the great man has a dream/vision (usually before he attains great-man status) and sees a dragon eating a lion eating a mouse, or something like that. None of us ever have dreams like that. Personally, I've rarely had any dream that had anything resembling a clean, clear-cut narrative, let alone a 'symbolic' one. Yet these stories pop up quite persistently in all sorts of places: Antiquity, medieval mysticism, Chinese Folklore,... They're also quite prevalent in the collective Native American imagination as late as the 19th century, I believe.
What's up with that?
A: They are completely the result of literary 'tidying-up' efforts on behalf of chroniclers, historians,... They don't correspond to any real experience by anyone ever.
B: People did have dreams like that, largely because they were socialized in a way that led them to expect their dreams to look like this. This implies the existence of a social 'repertorium' or even a 'collective unconciousness', such as also is suggested by the existence of culture-specific
disease-patterns. C: People may ahve ahd dreams like that, but that was the result of environmental factors, and they had their causes in the physical world. (=die-hard physicalist option)
D: Just yesterday I dreamt of a Snake eating its own tail and my great-great-great-grandfather gave me advice on my professional life.
(FTR, C and D are only in there for completeness' sake. The real question is whether you think there may be some truth to B)