"Chunking" describes how human memory utilization works. It is important to remember this concept as we look at doing several tasks "simultaneously". We are in fact switching between them rather than doing them at the same time [...].
You are on the phone when someone walks into your office. They ask for your advice or a decision. You stop listening to the person on the phone briefly, scan the note in front of you, scribble a response and go back to the phone call. You did not do the two activities (phone call and in-person conversation) at the same time. You actually did three tasks in sequence; started the phone call, had the in-person conversation, and then resumed the phone call. [...] you could have gotten both of them done better, and in less total time, if you had done them one after the other instead at the same time. The reason is that as you begin each task you have to focus on it and get started.