Oh, my friend, you are unlocking a huge warehouse full of secret knowledge. I sincerely doubt we can cover even the most interesting bits.
Here is a taste:
"Reasoning was not designed to pursue the truth. Reasoning was designed by evolution to help us win arguments. That's why they call it The Argumentative Theory of Reasoning. So, as they put it, "The evidence reviewed here shows not only that reasoning falls quite short of reliably delivering rational beliefs and rational decisions. It may even be, in a variety of cases, detrimental to rationality. Reasoning can lead to poor outcomes, not because humans are bad at it, but because they systematically strive for arguments that justify their beliefs or their actions. This explains the confirmation bias, motivated reasoning, and reason-based choice, among other things."
That's from:
https://www.edge.org/conversation/hugo_mercier-the-argumentative-theory where there is a nice video clip embedded discussing the Argumentative Theory.
My interest in rhetoric is as a commercial writer. My job is to cajole, inspire, motivate and persuade. We no longer call it rhetoric though. We call it purposeful communication. A sort of secret science, full of alchemical BS as well as useful techniques.