Overstocks and out-of-stocks cost retailers $1.1 trillion globally. While inventory management has always been an issue for retailers, the problem has been exacerbated with the advent of e-commerce and increased access to substitute products. Shoppers are becoming increasingly difficult to serve as they expect retailers to provide more product variety and higher levels of customization all at lower prices. The result: it is harder now than ever for retailers to maintain healthy inventory levels.