I thought I knew my brother Mike pretty well. He and our brother Pete and I were very close in age – Mike was born two weeks before my first birthday and Pete was born 11 days after my second birthday – and growing up it was always “marymikeandpete,” as though we were one person. In childhood we spent most of our waking hours together. Together we explored the nearby woods and fields, caught turtles and pollywogs, played ball, rode bikes and made up endless games. Until I was about 8, we shared one bedroom.

By the time I was 10, we had moved four times – bouncing among schools, having to get used to new situations and people…