People believe they can multi-task because the body can do a physical activity and a cognitive activity at the same time. So people are able to walk and talk, run and listen to a book etc. The brain does not do two cognitive tasks at the same time. The brain switches between tasks, very quickly. Every time the brain switches task it must determine how much of the task has been completed and what the next step would be and then continue with the task. This time contributes to the slowing down of completing the two tasks. If the brain works on one task at a time it completes it without delay. Try it, put an article in front of you and something to write. Do them both at the same time and time how long it takes you to get the two tasks done. You will notice that you will keep going over the material to see where you left off as your concentration shifts between the task. Next do each task separately and time how long it takes to complete both task. In order to stop multitasking, plan your work schedule and remove the distraction of other work, e-mails, twitting, phone calls, televisions, music etc.