Agreed, and doing Summer Stock, Regional Theater, Non Union tours, etc, a lot of the times you don't have an understudy or the luxury of calling out and just have to "figure it out."
Not pointing blame at either people here, but I do think it's a matter of proper training.
Same goes for people who said it's too emotionally demanding. I, personally, don't think that's a thing when you take in shows like Caroline, or Change, The Inheritance, Angels in America, etc. All much bigger, emotionally heavy and demanding shows.
Again, as a seasoned performer, you learn how to deal with these emotions. I remember being in college and seeing an upperclassman do a production of "The Seagull." The lead actress was in tears during the final scene, and all through curtain call, and then again backstage after. I remember years later playing George in "Our Town" and the director telling me you have to control your emotions because you might be having a huge breakdown in one scene, and then next scene is 5 years later and you're fine. So, sure, it might be emotional and heavy, but as an actor you should not be putting that on your shoulders. It's ACTING. You're pretending to take on that emotion. Just my thoughts.
Xoxo Gossip Girl