TPIEF provided a training course for interpreters this past Sunday (12 March) which I had the opportunity to attend. I don't normally go to these, so it was an unusual chance to see what kind of skill is actually required to be an interpreter.
The most difficult exercises were training for simultaneous interpreting, which I have never attempted. In one exercise, a recording of vocabulary was played, after which we were to repeat each word two or three words later, so that we were required to retain each new item while recalling the others. Then there was a sample of text which we were to repeat line by line and then translate. There was also a truncated system of note-taking (comprised of abbreviations, characters and symbols) by which one could, if sufficiently versed in it, preserve all the essential details of quite lengthy passages and translate them with perfect accuracy.
I've heard that simulaneous interpreters in government only work for shifts of about two hours, because the human mind is completely exhausted at that point. I've been so exhausted I've lost consciousness just doing consecutive interpreting all day long, and that's a lot easier. All in all, Sunday morning was a mental workout. It was similar to physical exercise that recruits muscles one didn't know one had.