One day a family of four (mother, father, and two kids) started a new collection. The collection grew as the days passed, and at the end of the week, content with their efforts, the father placed the collection in its entirety on display just outside the house. While the family slept, however, a few men drove up and swiped the whole collection before simply driving away. The family didn't know any of these men, and the men, likewise, had interacted with neither the parents nor the two children ever before. The following morning the family awoke and discovered the collection was missing. Unfazed by and even rather pleased with the turn of events, the family again teamed up and worked together on a brand new collection.
Why wasn't the family upset?