Genetic influences on personality are something that you can't take credit for. But if those geans shape our biology in such a way that we are more likely to be persistent, or delay gratification, then that ring between agency and credit starts to get muddled. This is an idea resusntin none of the precepts of justice tend towards desert, right? Tend towards rewarding desert, because it's impossible at a certain point. It does suggest that any efforts to arrange a social order, to mete out rewards according to what people deserve, is rapidly run into a point of comere impossibility.