Sei Shonagon’s Pillow Book—a key inspiration for Rivka Galchen’s new book — contains a list of “Things That Make One Nervous.” And wouldn’t the blessed event top almost anyone’s list? Little Labors is a slanted, enchanted literary miscellany. Varying in length from just a sentence or paragraph to a several-page story or essay, Galchen’s puzzle pieces assemble into a shining, unpredictable, mord...