Homer and Lisa go to the Springfield Museum, but Homer isn’t sure he understands the entrance policy. He checks with the attendant, but doesn’t know why anyone would want to pay the suggested donation when they could go in without paying anything. Because the museum is available to everyone, regardless of whether they pay, it operates similar to a public good. The problem? Public goods are subject to free riders, like Homer.
Asrar Chowdhury has a great summary of this episode on The Daily Star as well.