Have you ever thought about what makes self-storage companies so successful? It's not just because these businesses serve a practical purpose; they are also tapping into an aspect of American life that is all about the ups and downs of our relationships with our things. We are a populace of pack rats, and there are many reasons why we hold tightly to what we own—even when a portion of it is portable, boxed up, and crammed into a unit that, in some cases, is taller than the former occupant.