Emily Rapp was born with a congenital defect that required, at the age of four, that her left foot be amputated. By the time she was eight she'd had dozens of operations, had lost most of her leg, from just above the knee, and had become the smiling, indefatigable "poster child" for the March of Dimes. For years she made appearances at church suppers and rodeos, giving pep talks about how normal and happy she was. All the while she was learning to live with what she later described as "my grievous, irrevocable flaw," and the paradox that being extraordinary was the only way to be ordinary....

What does it mean to be a success? To be a good parent? To live a meaningful life? Emily Rapp thought she knew the answers when she was pregnant with her first child. But everything changed when nine-month-old Ronan was diagnosed with Tay-Sachs disease, a rare and always-fatal degenerative disorder. He was not expected to live beyond the age of three. Rapp and her husband were forced to re-evaluate everything they thought they knew about parenting and to learn to parent without a...