Why do you think Walls opens the book with this story?

The memoir's beginning lays bare all of Jeannette's hitherto pent up insecurities about her troubled past. Though she has escaped the substandard circumstances that characterized her childhood, Rose Mary's appearance by the dumpster is a symbol that Jeannette cannot ever fully hide from her past life of poverty and periodic homelessness. The story and the fear of it being discovered could always be lurking behind any city corner.