I tend to chalk the occasionally-violent reactions up to the fact that actors are under much, much more stress than production people generally are.
If I screw up, odds are good that nobody outside the company will ever attribute it to me, and--barring a truly epic error--even those within the company will forget it within a few days. Barring a significant disaster (we're talking loss of life), it won't affect my career substantially. Even if it does leave a dent, I can (comparatively) easily just slip downmarket a little, or move to another location, or to another type of theatre, and escape it. I happen to live in a union city to boot, so anyone on the tech side of the big leagues really has to screw the pooch before they stop getting called.
Actors, by comparison, have to wear all of their errors. Their castmates will remember, and--if they're unkind--will remind them. The audience will know. In fact, if a technician makes an error, the audience will probably subconsciously blame the actors. When the play's just plain bad, the public almost invariably "blames" the actors, who will have to wear the play around their necks for the rest of their careers. Directors, playwrights, designers, and--yes--technicians and stage managers get off scot free by comparison. Considering that the actors are also the only members of that group who are completely dependent upon subjective decisionmaking and perception in order to get continuing work, this must be a major concern for them.
We might also consider what's going through an actor's mind during a run.
- What's the next line?
- What's the blocking?
- What's the inflection and accent?
- What's the body language?
- What's everybody else's blocking and body language?
- Did he just skip a whole paragraph? Jeez, where are we?!
- Is that my mother-in-law?
- Is that the guy from the Tribune?
- Okay, what's the next line?
- Diction! Diction!
- Just imagine them all naked. See? All naked.
- Christ, this audience isn't laughing nearly enough.
- Oh god, that is my mother-in-law!
- And now she's naked! Ew ew ew!
By comparison, as Mr. Shiner teased out, the booth allows us to be fairly mechanical: a good SM will always be thinking ahead and anticipating, but the basic process boils down to "read line, say cue; read line, say cue". (The technicians have it even easier: "hear cue, push button; hear cue, push button".)
And if and when unexpected things happen?
1) We're rarely in any immediate danger. If the set collapses, or a fly line goes out of control, or the effects go all wonky, or whatever else, we're safely ensconced in a tiny room in a completely different part of the theatre.
2) We usually don't have to wear it. (See above.) We should still learn from it and seek to improve, but it's probably not going to be a stain on our careers.
3) We have protocols and training and practice and rehearsals for exactly these situations. If we're any good at what we do, we're never actually ad-libbing: we've worked through countless scenarios, we know exactly what we should do (guided by industrial best standards, thorough documentation, personal experience, discussion with colleagues, etc.), and we know exactly what everybody else should do. Actors, by comparison, are essentially thrown to the lions when things go pear-shaped.
