ADHD Brains often have trouble prioritizing important tasks over smaller less demanding tasks. This isn't a matter of laziness. To the ADHD brain, this would just make practical sense since getting more tasks done seems like it would be much more efficient. By doing this you get more on your "To Do" list checked off. Checking items off that list then gives the brain a shot of Dopamine as a reward. This creates a cycle of wanting to do less intensive tasks to get that reward over the more complicated task.

There are multiple factors that can come in to play when it comes to this.

Difficulty

People with ADHD often look at things from a big picture perspective as opposed to the process. They can see the final outcome, but often struggle to start because the task appears too daunting or difficult. The lower-priority task is frequently less physically and mentally taxing than the higher-priority task. Getting the lawn mower out of the shed, starting it up, and pushing it to the grass is a less cognitively demanding job than filing taxes, which is a nebulous and psychologically difficult activity. And it also gets part of the "To Do" list checked off.

Autopilot

Tasks with a pre-existing "menu" are more likely to be completed. Laundry and other home activities that can be done on autopilot fit under this category, but research paper writing does not. Thus, the autopilot tasks tend to get pushed to the forefront and items get checked off, while that research paper sits collecting dust.

Time Frame

Autopilot jobs often have a more precise and predictable time range; there is little ambiguity about how long they will take. While it may take 10 minutes to delete unread e-mails, the same cannot be true for planning a significant upcoming project for work. It will be far more efficient to clear out emails and even respond to a few of them (thus completing something and getting that sacred check mark) than to begin a large job that appears to take an eternity.

Task Progress

Autopilot jobs frequently have a distinct beginning, middle, and end. Mowing the lawn begins with removing the mower from the shed, and you're halfway done after you've clipped half of the grass blades. It all comes to a close with the mower returning to the shed. With each of these progress markers, the brain is able to mentally check something off a list, thus feeling that sense of reward from the Dopamine. A task like studying for a final test, on the other hand, does not have clear success markers; it's more difficult to know if and how much progress you're making.