A childhood belief about getting pregnant

I asked my Mom how She and Dad decided to have me as a baby. She said, "Oh, we just knew", and changed the subject (i,e; I was unexpected). So, for years after that, I just thought grownups would look at each other, raise one eyebrow, and bam, the woman was pregnant. Then I deduced from that, that if I followed a girl around at school long enough, she would become pregnant.