I have never been formally diagnosed with any kind of attention deficit disorder. I also am not any kind of a medical expert on the subject (or any medical subject for that matter).
That said, I believe we live in a society that makes paying attention to a single task difficult, if not impossible. TVs with 100 channels and a remote to allow quick flipping. Pop up ads on the Internet. "Story" links at the bottom or on the side of the current article we are reading. (Story in quotes because many times it's a link to a slide show that wants you to click 30 times to find out the 10 foods you should avoid - it's not a story, it's a per click revenue generator).
And the above is a perfect example of what I mean. With so many inputs coming at us - focus is at a premium.
One thing I'm trying is what I call "Anchored ADD". I have one task to do - that's the anchor. There are other things that may pop in my head while I'm doing that task, so I work them in or process them somehow. All the while, I'm anchored to the first task.
For example: After dinner I remember I need to pack my workout clothes for tomorrow. That becomes the anchor task. I go to my car to get my workout bag. While I'm in my car, I see a coffee mug. I grab the bag, and the mug. On the way to my bedroom closet I drop the mug in the sink. When I get to the bedroom, I see some clothes that need to be put away in the closet. I grab them on the way. I pack the gym bag. On the way back out of the bedroom I notice a water glass. I pick that up and take it back to the kitchen.
That's a small scale, simple example. In reality, there might be 4 or 5 more things that wind up happening while I'm still anchored to the big task. I have my iPhone with me, because I frequently notice things that need to be done later. I ask Siri for a reminder.
In the end I have accomplished the main task, but also knocked out a few others, or at least processed some inputs for later action.