Have you ever thrown something away and later regretted it? I read a news report recently about a grand piano that was going up for auction. This piano once belonged to John Lennon, the lead singer and songwriter for the Beatles. Before his death, he gave it to a friend. The friend loaned the piano to a local school. Someone at the school—who obviously didn’t know the piano’s famous first owner—sold it off with a bunch of old pianos for a grand total of $3,000. Fortunately, someone realized the piano’s value. It is expected to sell for $3 million at auction. (1)

We all have a few things we wish we hadn’t thrown away. Maybe nothing that is famous and valuable, but things that mattered to us. But most of us have the opposite problem: we keep a bunch of stuff that we should throw away instea…