Our sense of attachment to things is connected in our brains to our sense of self in how we see the world. Because of this connection, our brains hold things we own in high value as part of ourselves. This begins from a very young age and carries through adulthood, never really going away, as observed by Jean Piaget, a child psychologist, with young children reacting overwhelmingly strongly to items they want or think are theirs.
However, this effect does seem to have developed with the developing world. A study of an isolated egalitarian society-based tribe in northern Tanzania showed no emotional attachment to items, possibly due to the fact that they do not have individual ownership of things. On the opposite spectrum, hoarding is a disorder where people have an over exaggerated feeling of responsibility and attachment to their things to where they cannot let anything go. As the world moves to a digital age, where things are becoming less and less relevant, it will be interesting to see where our minds evolve with our attachments.