“He awoke—and wanted Mars.” 

Using the opening sentence of the story to illustrate Quail’s most pressing desire shows the reader how urgently Quail yearns for Mars. Though the reasons for Quail’s obsession shift and change depending on his memories, the immediacy of his desire never changes. 

“After all, an illusion, no matter how convincing, remained nothing more than an illusion.” 

The disparity between illusions and reality is a central idea in the story. Before visiting Rekal, Quail thinks he understands reality. But given the choice to escape his boring, miserable life, Quail jumps at the chance—and his decision fractures the nature of reality for the characters and for readers. The substantive reality for Quail now depends on whatever illusions are implanted in his mind. 

“He rose, came over to shake Quail’s nervous, moist hand.” 

Quail is a nervous and awkward office clerk. When he meets a smooth-talking businessman like McClane, Quail is intimidated, quickly buying Rekal’s implant package despite concerns about its cost. However, as soon as Quail becomes his next incarnation, a government-trained assassin, he will completely change his demeanor, fully embracing a false reality that shows the efficacy of the fake memories.