Wiktionary
n. (context idiomatic English) The reasons or motivations for a fact, action(,) or decision, (non-gloss definition: especially) the complete set of such reasons or motivations.
Usage examples of "whys and wherefores".
For the next hour the three men talked, each telling his story, and trying to explain the whys and wherefores of what he had seen.
Delving into the whys and wherefores of the great Kicksey-Winsey was blasphemous and would call down the wrath of the clarks-the ecclesiastical force on Drevlin.
A part of him wanted to try to make sense of how this effect might work, to puzzle out the whys and wherefores of virtual sirens—.
Well, I'm satisfied to learn the whys and wherefores of his Gift, and what Kalira can do with it.
Dad had told them that ages ago, although not the hows, whys and wherefores.
He tagged along and I explained the whys and wherefores of every step in the job.