Once when I was eight years old, my hair caught on fire. My older sister saved my life by shoving me out the front door and burying my head in the snow. We were never close, thanks to an imaginary line my mother had drawn between the obedient, dependable daughter (me) and the obstinate, wild one (my sister). But that day, we sat shoulder-to-shoulder on my sister’s bed, counting the minutes in dreaded silence before our mother returned home to discover what had happened.