A lifelong inability to put down books + the sixth grade. We were "preparing for junior high school", and instead of having a single class all day through, all the teachers in grade six did "rotations". So once a week -- I think? -- our class would get rounded up and shipped off to another teacher's room, where we'd learn about science, gym and/or a section of history. My teacher gave us Greek mythology, which I ate up. Another gave us Egyptian, and a third touched a bit on Jewish mythology via the Holocaust.
At the time I recall being pretty fond of Persephone's tale (ah, to be twelve again with giant rose-tinted reflective lenses), as well as Pandora's -- she's half of my namesake, so. The interest in mythos, history and theology has bordered on lifelong, so it was kind of like giving a bottle of rotgut to a kid with Fetal Alcohol Syndrome. That combined with growing up on comic books spelled D-O-O-M out rather concisely.