Girl with a pointy hood and white schoolbag at the curb, N.Y.C., 1957.

“Arbus was particularly sensitive to children,” the curator Jeff L. Rosenheim said. “They’re in the process of changing their identities as they grow. She’s at the curb — the curb itself is that liminal stage.”

In his classic study of the short story “The Lonely Voice,” the Irish writer Frank O’Connor identified the primary difference between the novel and the short story as one of belonging. Novels, to put it simply, are about people trying to fit into society, while stories are about the loners, the outsiders, the kooks, those to whom society “offers no goals and no answers” and for whom the short story’s “intense awareness of human loneliness” is perfectly suited.

From practically the moment that the commercial photographer Diane Arbus set out to become an artist at the ripe age of 33 — numbering her negatives sequentially from 1 to more than 6,000 before her suicide in 1971 — she seemed to know that the story of the outsider was her intellectual inheritance. And she had the uncanny ability, in a city as crowded as New York, to isolate even those who thought they belonged, to find them almost alone on a sidewalk, their eyes searching hers — later ours — fiercely and uncertainly through the camera.

“Diane Arbus: In the Beginning,” which opens July 12 at the Met Breuer, will give the first real glimpse of one of the greatest artists of the 20th century in chrysalis. Drawing from the Diane Arbus Archive, acquired by the Metropolitan Museum in 2007 from the artist’s daughters, Doon and Amy Arbus, the exhibition focuses on the years 1956 through 1962 and includes mostly images that have never before been exhibited or published, a huge body of work predating the pictures that have defined Arbus’s career. The show will arrive just after the publication of “Diane Arbus: Portrait of a Photographer” (Ecco), a highly anticipated and unauthorized biography by Arthur Lubow, a contributor to The New York Times, that delves deeply into the connections between Arbus’s work and her sometimes troubled life, in interviews with many friends who have never before spoken publicly about her.