It’s easy to get caught up in exciting, fresh ideas. They are surely more important than the dreary stuff in your back catalog!
Closure is important. Whether you complete the task or not, finish the task. If you don’t want to complete it, discard it. Don’t leave stuff hanging, it will become death by 1000 papercuts once you have 3 or 4 projects hanging over you, unfinished. It will become sludge that you get stuck in, quicksand that makes it impossible to move on to the next project.
At work, it is especially important since a lot of the tasks you do will not be “fun” or “revolutionary.” They are simply tasks that make cogs in a bigger machine. Once you have 3-4 dreary projects lined up behind you with no motivation to finish, you end up overwhelmed and unable to focus on just 1 of them. This is a horrible position to be in and can be difficult to climb out. Not only do you feel intrinsically bad about not finishing the task, you will not be able to move forward on any exciting task. So it will end up making your work life miserable because all you have to work on is boring, uninteresting stuff.