Guarding Your Investment, Keeping Your Children Profitable was an ancient Ferengi medical text, written by Doctor Posck of the Ferengi Wellness Institute, as a guide for raising Ferengi children. The book addressed such topics as excessive and compulsive oo-moxing in young children, and dealing with a child's Attainment ceremony. The chapter on the Attainment ceremony was used by Quark as an illustration of the 21st Rule of Acquisition, "Never place friendship above profit." (DS9 reference: Legends of the Ferengi)