Lucia dos Santos was born in 1907 at Aljustrel, a hamlet in the parish of Fatima, into a farming family, and was ten years old in the summer of 1917 when she and her younger cousins Francisco and Jacinta Marto were pasturing sheep at the Cova da Iria. What the three of them reported over the following months is the subject of the Fatima devotion; what distinguishes Lucia from the other two is simply that she survived it.
Francisco died in 1919 and Jacinta in 1920, both in the influenza pandemic, both still children. Neither left a written account of their own. Lucia lived until 2005, and for most of those years she was the only person alive who claimed to have been present. That single fact reshaped her life. She was removed from the district as a girl, partly to spare her the crowds already gathering at the site, educated by the Sisters of Saint Dorothy, and eventually entered the Carmelite order, spending her last decades enclosed at the Carmel of Saint Teresa in Coimbra.
The asymmetry matters for anyone reading the Fatima material. The two children who died young are remembered almost entirely through what others wrote about them. The one who lived became the source, and so the tradition's account of all three passes through her.