One thing that a lot of people seem to misunderstand is the fact that the castbar shows what the BOSS is doing, not what you need to do to counter it. When he casts "Divide by three", that means the boss is trying to divide by three. Think of it the same way as the second boss in Temple of the Fist: When he casts "Fore and Aft", he isn't telling you to go to the fore and/or aft. He is telling you that he will be attacking at the fore and aft.