So I don’t forget it, you might say? Sure, your memory cannot hold as much information or hold it as reliably as a piece of paper or a computer can, but writing things down has scarier downsides than just forgetting.
First, with a mental to-do list, we cannot prioritize them and lose perspective. We can remember our todo list for today, but doing mental operations on it – such as adding detail to task descriptions, tagging, reordering – becomes too much. We also cannot remember the tasks that we have completed (more on this later), the tasks we need to complete in the longer run, so we naturally lose perspective and start prioritizing urgent tasks over important ones (just because these are the ones that we remember). Any new task comes with an urgency bonus, and the mental strain of keeping the todo list in mind prevents us from reevaluating it, so we end up ‘putting out fires’ in an endless loop rather than tacking important stuff such as development.
Second, we get (a lot) worse at thinking. Keeping anything in memory is a huge cognitive load. Try it for yourself: pick two similar math problems, measure the time it takes you to solve one, and then try to memorize a list of something and solve the second problem while keeping the list in mind. You’ll have a hard time concentrating, you’ll probably spend more time, and you’ll feel more tired.
Third, we are less motivated to do the tasks on the list. Because of the high cognitive load, the task seem harder than they actually are. Besides, due to the Zeigarnik effect, we only remember the uncompleted tasks but forget the completed tasks, which makes it aways seem like we have done nothing, which brings our motivation further down.
Fourth, we cannot relax. Due to the same Zeigarnik effect, we remember uncompleted tasks until they are complete. You leave work but your brain keeps thinking about it, so you can never relax.
By keeping your todo list in your read, not only are you risking to miss some of them, but you also cannot use any productivity techniques or avoid cognitive distortions, you are killing your motivation by keeping the cognitive load high, and leaving yourself no chance to recognize or even remember your successes. In addition, you are using more energy to think, you are less creative and less productive, and on top of all that, you are not letting your mind relax and recover. So don’t keep anything in your head, write it down even just on a post-it note: this simple action will remove most of the mental stress, give you a boost of motivation and make you happier and more productive.