This article by Charles Isherwood discusses how often one can go to the Broadway theater and find out that the star you came to see is out and the understudy is on. I think his premise is a bit overstated, and the piece lumps together stars who miss shows because they have movie and TV projects with stars who miss shows because of illness. He also exaggerates a bit when he says, "[Ethel] Merman appeared in a new show almost every season." Ethel more often skipped a year between shows. But otherwise, it's a good essay. (If you're interested, I wrote a piece about this that's posted here.)