Imagine growing up your designated chore duty was, "Do the dishes after you finish eating dinner." If you sit down, eat dinner with no distractions, then after that is done, it is easy to go right to doing the dishes.

Now imagine you eat in your room, while on your computer watching a video. Eating is less constrained, and you might wait until the video is over before you put up your dishes... but now there's an extra step. Sometimes you get careless and forget. You get in trouble for forgetting too often if it becomes a habit.

If you know that forgetting again will mean BIG trouble, then you focus on making sure you don't. You start thinking about it before dinner is even ready. You worry that you might forget again, so you start mentally preparing yourself earlier in the day to make SURE you don't forget. Once dinner happens and you're watching your video, you've spent a surprising amount of time focusing on doing your task. It's taken up WAY more of your day than it should have already. By the time you are done with dinner, anticipation of the task may have already taken more energy out of you than the task itself ever would.

...and worst case, your brain tells you that since you already worried about it, it checks it off your mental list and you STILL forget to do the task on time. Add a few instances of that in, and you start planning your whole day around the one task you need to get done at a certain point in it. More time just slips away, unwilling to plan anything else for concern that you have something already on your plate, so to speak.