We live in Distractionlandia, with a thousand things clamoring for our attention - certainly from that device in your pocket if not from the back seat of your car. The pull to do 2, 3, 4+ things at once is ever-present, including for those of us who are supposed to know better. We multitask with and without awareness of doing so. Some people claim that they're more effective when multitasking. I used to be one of those people, but not any more.
While I still find myself multitasking all too often, it does help to understand what's really going on in the brain. Notice, refocus on one thing at a time. Notice, refocus. Lather, rinse, repeat.
Dr. Sanjay Jupta, a truly great explainer, on multitasking.