Ever noticed that we love to rummage through other people's stuff? There is an entire sub-culture dedicated to flea markets, swap meets, yard sales and consignments. Some families, like my own, have family members who would never show up to a family get together without the ubiquitous bag of items with the preface "I can't or don't want to wear these anymore, so you can have it". There are all kinds of reasons humans exchange stuff. Some of the newest and hippest designers take pleasure in re-fashioning found items or reconstructing used clothing.
Whatever the reason or the intent, it is simply good for us and good for the planet to get in the habit of 'moving it on' and sharing things we don't want with others.
