Four People

Their names were Everybody, Somebody, Nobody and Anybody.

Whenever there was an important job to be done, Everybody was sure that Somebody would do it.

Anybody could have done it, but Nobody did it.

When Nobody did it, Everybody got angry because it was Everybody's job.

Everybody thought that Somebody would do it, but Nobody realized that Nobody would do it.

So consequently Everybody blamed Somebody when Nobody did what Anybody could have done in the first place.