I get it now.
An audience member, may, at any time, stand up and join the play.
At that point the barrier between audience and play dissolves.
And, since that barrier is so easily breached, it is not real.
It is an illusion.
The audience sits there politely pretending that what is in front of them is real. That makes it real.
If you were to ask one thousand scientists if global warming was real and nine-hundred and ninety-eight of them said it was, you’d believe them, right?
Like any thinking person would?
Likewise, ask one thousand audience members if the play in front of them is real.
Ask them by watching them gasp, laugh and cry.
For them, the show is real.
By the consent of the audience, plays are real.
That makes writing them easier, I think.