This is why, even with classical theatre, I'm trying to stay completely spoiler free. Not too long ago I attended the theatre and ten minutes before the play was due to start, the audience member behind me began reading a full synopsis of the play she'd pulled from the web. I sat with my fingers in my ears.
In the end I left the performance at the interval. It was an awful production and I decided that I'd save the ending for a version I was enjoying.