Human beings are thinking creatures. In order to write about human beings in a complete fashion, one needs to write about how human beings think. The ability of language-based stories to depict thought is precisely what keeps them competitive in a world flooded with stories. Human thought reacts to its environment. Writing accurately about the way people think therefore involves writing accurately about the environment in which people live.
Human beings live surrounded by information.
To write completely about human beings therefore means taking on the duty of writing about information. The human mind references its own memory banks incessantly. Writing that seeks to document the human mind will reflect this. The literary device of the extended flashback is not an illustration of the way we actually experience memory. We live in a perpetual wash of microflashbacks.