For years I've been telling anyone who'll listen that multi-tasking is a nonsense. Good to read that my feelings/views on the subject are borne out.
The body can only do as it's told which means that it responds to any thought or feeling we have. Try this at home if you like but what I've just said that be proved by banging a nail into a wall with a hammer. If while you're holding the nail steady as you hit it you allow your mind to wander chances are you'll hit your hand or fingers.
All thinking is directional - in my view, that's what thought are for, for directing the flow of energy.
The flow of energy is naturally wild but we can control it to suit our objectives. For example, it's like driving driving a car. To drive forwards you shift the gearstick into gear (or the automatic does it for you). To drive backwards (which strictly isn't backwards but forwards since you'd normally turn your body around to see the direction in which you're heading), you have to first come out of forward gear then go into neutral before engaging the reverse gear.
All feeling is harmonious. Hence, the combination of thought and feeling maintains balance and harmony. Anything that happens to interfere with the subtle link between thought and feeling will cause an upset or confusion at psychological level. Confusion is simply thought and feeling in a muddle, which is why straightening out gets oneself together. Attempting to do more than one thing at a time (so called multi-tasking) cannot be done because our internal systems aren't able to go in in more than one direction at a time.