Kató Lomb describes some of the difficulties of being a simultaneous translator:
When a speaker recites intricately polished, long sentences from his script and we have to improvise, then a wrestling match between speaker and interpreter ensues. All we can do is wrestle in the Greco-Roman style while the speaker does so in a “catch-as-catch-can” way. In this struggle, we are always defeated.
… Anyway, only the speaker is allowed to stop. (“A profound mind, searching for the most suitable form to express his thoughts!”) If it is the interpreter who falls silent, then the sudden silence will awake even the delegates peacefully napping in their headphones. (“There are amateurs sitting in the booths; they don’t know the terms.”)
—Kató Lomb, Polyglot: How I Learn Languages [Download PDF]