The brain feels a desire to return to incomplete narratives, unresolved problems, unanswered questions, and unachieved goals because it craves cognitive closure (Zeigarnik effect). It means that it will be "working" in the background until it will find.
Another consequence of the Parkinson law is that we tend to speed up if we have the finish line in sight (it's also related to the Zeigarnik effect – the mind craves closure). Creating such 'boxes' for your inputs creates mini finish lines which accelerate your efforts. This means that the most important step is to get started. Once you're inside such a 'box,' your brain will focus on getting to the finish line as effectively as possible.