It served as a psychological hack that motivated and inspired its users.

But when users asked for and received a feature that served as a traditional to-do list, the app's popularity decreased. As busy professionals, who have all utilized to-lists, we can glean from the trajectory of Chen and Guzman’s productivity tool why to-do lists work, why they often don't work and how to get the most out of them.

Why to-do lists work: Soviet psychologist Bluma Zeigarnik studied a unique quirk of the mind and found that when a task is unfinished, humans constantly think about it to keep it from vanishing from our short-term memory. It is known as the Zeigarnik effect. To-do lists help us avoid the Zeigarnik effect by allowing us to focus on other things without our outstanding obligations breaking our concentration.

Why to-do lists don't work: Just because we got the task out of our head and onto paper doesn't mean it gets done. If there is no plan or timeline for completion, the to-do list grows and becomes a daunting assignment for your future self to complete.

How to get the most out of your list: One helpful approach is to add a plan for how you will execute the tasks on your list and only add items that can be completed in a timely manner. Otherwise, your to-do list becomes an ever-growing list of shame that is both daunting and demotivating.