My Grandpa Tom grew up in rural southern Illinois, but spent some time near Chicago due to his job with the railroad in the late 30's, which is how he became a Cubs fan. In the 40s, he and my grandmother moved to North Dakota, where they have remained ever since, and there is no local baseball team. So my grandfather remains a Cubs fan.
My father's the major reason I fell in love with the Red Sox and Patriots, but he believes strongly that, as he puts it, "you always have to root for the home entry." In other words, if my sister and I had grown up where my mother grew up, rather than where my father grew up, there's a good chance we'd be Cubs fans.
Then there is my friend Brian. Over the years some of my most impassioned, intense debate over baseball has been with him. We have gotten into the deep groove about its cultural meaning as representative of a city, about the fundamental philosophical differences between Red Sox and Cubs fans -- which are surprisingly many, at least to me as a Red Sox fan, and presumably would be to several national sports broadcasters, if they were paying any attention.