All the best performers bring to their role something more, something different than what the author put on paper. That’s what makes theatre live. That’s why it persists.

Sondheim is emphasizing theatre’s essential liveness: a script is not the finished artwork but a set of instructions that must be embodied. Great performers do more than reproduce what is “on paper”; they contribute imagination, timing, physicality, vocal color, and psychological nuance that cannot be fully notated. The remark also implies a collaborative view of authorship—playwrights and composers create the framework, but actors complete the event in front of an audience. In this sense, theatre persists because each performance can be newly made, with interpretive choices and human presence generating freshness and immediacy that resist becoming fixed or purely archival.