The best financial planner Michelle Singletary ever knew was Big Mama, her grandmother. Big Mama raised Michelle and her four brothers and sisters on a salary that never reached more than $13,000 a year. Yet at her death, Big Mama owned her own home, had paid off a car loan, and had a beautiful collection of Sunday-go-to-meeting church hats and a savings account that supplemented her Social Security check and small pension. Most important, she had...