The phrase, "One man's junk is another man's treasure" is an idiom people use to point out that what one person views as useless, another person might highly value. For example, one person may see no beauty in a painting, while another sees it as a brilliant piece of artwork. A rich man might throw away an old television set to upgrade to a new model, while a poor man is excited to find the old set in the trash.
Variations on the phrase, "One man's junk is another man's treasure" appear in the lyrics of several songs. An example is the song "Thrift Shop" by Macklemore. In the second verse, the song states, "One man’s trash, that’s another man’s come-up," implying that one man might feel he has come upon something great after discovering an item that another man donated to a thrift shop.
Another example is the song "One Man's Trash" by Marty Robbins. In the song, Robbins sings, "Why don't you tell me what that boy has done to you? I said one man's trash is another man's treasure." He addresses his words to a woman whom another man has hurt, implying that he views her as valuable even if the other man does not.