Some works of art can be so precious and intimate in their appeal that you just have to own them. That impulse is what fuels the art market and, on a less exalted level, it is what keeps music collectors searching for ever purer forms of recording. Art here becomes a private affair, something special between you and it, and the rest of the world can go hang.

But the opposite effect applies too. Some experiences are so great that you want to tell the whole world about them, so that they can share your joy. In fact you can't stop talking about them. I feel that way about The Wire , HBO's devastating police series that has just started its fifth and final season in the US.