This myth is based on the assumption that human beings are capable of doing two cognitive tasks at the same time. We’re not. Instead, we learn to move rapidly between tasks. When we’re doing one, we’re actually not even aware of the other.
If you’re on a conference call, for example, and you turn your attention to an incoming email, you’re missing what’s happening on the call as long as you’re checking your email. Equally important, you’re incurring something called “switching time.” That’s the time it takes to shift from one cognitive activity to another.
Therefore, never read emails while in meetings!
According to researchers switching time increases the amount of time it takes to finish the primary task you were working on by an average of 25 percent. In short, juggling activities is incredibly inefficient.
(Source: Tony Schwartz, author of “Be Excellent at Anything”)