What is the theme in A Life in the Theatre by David Mamet?

At the core of A Life in the Theatre is a tension between friendship and growth and development. In scene 1, the older actor Robert takes the younger actor John under his wing, befriending him. At first John welcomes the attention of the mentor, inviting him to dine with him after opening night and complimenting his performance. John takes Robert's cues and advice seriously, though he does keep much of life private.