“Zeigarnik found that our brains are wired to remember unfinished tasks better than completed ones. Like a to-do list, once we finish a task, our brain checks it off to free up mental bandwidth.
But this also means that, the more unfinished tasks we have running in the background, the more resources our brains dedicate to keeping track of them.”
Here’s an article about this:
The Real Reason Why You May Get Overwhelmed
Smuggling Grace 