Barring my Grandpa, I know very few people who use the Internet one page, or one tab at a time. Most people, like me, have multiple windows and multiple tabs open while we go about our business. For example I often go to a front page of a website and open all the pages I want to visit in new tabs.
This is why auto-play commercials and videos are incredibly frustrating and often self defeating. When I am watching a YouTube video on one page, and and a Vodafone ad starts to play on another, I am filled with nothing but hatred for Vodafone. Instead of enjoying my video, I have to hunt around for the bloody Vodafone ad so I can kill it. I pay no attention to the deal they are offering me, instead I start fantasising about cancelling my current contract. So please, advertisers, enough with the auto play ads already. You are only hurting yourselves.