In Shakespeare's Hamlet, the play-within-a-play is packed within a clear context and is used by Hamlet to send a message to Claudius. For us as the audience of Stoppard's play, however, the distinctions between a play and reality get totally jumbled. First, Rosencrantz and Guildenstern is nothing but a play on the stage. Secondly, it is a play that interacts with the action of an earlier play, Shakespeare's Hamlet. Third, it is unclear to what extent the Player and his Tragedians are driving the action of the play and to what extent the "real" characters are in control of what is happening. The difference between drama and reality is called into question, most explicitly in the arguments between Guil and the Player.
There is no one version of reality presented in the play, and the idea of one coherent reality is presented as a fiction. Only those that can act in a multiplicity of realities make it out of the play unscathed.