The whole world's a stage

Here's a charming metaphor which I fell upon describing life or, I suppose, the theatre of life(well, I'm assuming it's a metaphor otherwise the writer thinks we all actually live in a theatre) :

"Some people are working backstage, some playing in the orchestra, others are onstage singing. Some are in the audience as critics, others are there to applaud. Do you know who and where you are?"