Why does the plot of Rosencrantz and Guildenstern Are Dead start with a game of two-up?

In plays, the setting is often critical to orienting the audience to key elements such as time, place, and mood. Stoppard, however, describes the set of Rosencrantz and Guildenstern Are Dead as "without any visible characters." In the tradition of many absurd plays, Stoppard seeks to strip from the audience the illusion of certainty. Rosencrantz and Guildenstern enter a world full of uncertainty: their past is a mystery, their names seem interchangeable, and they must struggle for even the most fundamental knowledge of why they have been sent for. Rosencrantz's and Guildenstern's activity of tossing coins at the beginning of the play serves not only as an indicator of the paranormal nature of their world, but also as an example of how much of their existence is spent merely passing time.