Mind training is based on the idea that two opposite mental factors cannot happen at the same time. You could go from love to hate. But you cannot, at the same time - toward the same object, the same person - want to harm and want to do good.
I started with the book Boardwalk Empire and then immersed myself in the history of Atlantic City, World War I, the temperance movement, Prohibition, pop culture. I even read the news and magazines of the period just to soak in it. That was before I even started thinking of the story.