Letting go: why your brain clings to yesterday

Why a line from a cartoon holds up, and why letting go is still no easier for it.

“Yesterday is history. Tomorrow is a mystery. Today is a gift. That’s why it’s called the present.”

I remember exactly when that line first reached me. It was an evening with my boys, watching Kung Fu Panda. Master Oogway spoke the words and suddenly “today is a gift” felt like a key. A small piece of magic, tucked inside a children’s film.¹

Only much later did I look up who wrote it. The answer is that nobody knows. The most thorough quotation research finds the oldest complete version only in June 1993, in a speech at a school in New Jersey. The speaker credited an unnamed journalist. For the best-known attribution, to Eleanor Roosevelt, there is no evidence at all. It first appeared in 1999, more than thirty years after her death. And the cartoonist Bil Keane did draw a variant in The Family Circus in 1994, but not this line.²

For me that took nothing away from the words. In my living room that evening, beside my children, they arrived through a tortoise in a cartoon. That is origin enough.

And it is a truth that touches our lives. Because how many hours of today have you actually spent in today? Not in a rerun of yesterday, not in a worry about tomorrow, but in this moment?

What 91% of our worries can teach us

In 2020, researchers Lucas LaFreniere and Michelle Newman of Penn State University published a striking result in the journal Behavior Therapy. They asked 29 people with generalised anxiety disorder to write down every worry for ten days. Then they checked whether those worries came true.³

The finding: 91.4% of all worries never happened. Only 8.6% turned into reality. For some participants, not a single worry came true.

And here the nuance belongs straight away. This was 29 people, all of them with an anxiety disorder. So the number says nothing firm about you, and it is no proof that your worries are nonsense. What it does show is how our mind does its sums. We spend hours, days, sometimes years in meetings about disasters that never take place.

Why willpower doesn’t help here

Letting go is not a matter of pushing through. It is biology.

The American psychologist Susan Nolen-Hoeksema introduced the idea of rumination. In plain language: thinking in circles about what you feel and why, without anything changing. Her conclusion, after decades of research, is clear. Rumination does not make low mood and anxiety shorter. It makes them longer.⁴ It looks like working towards a solution, but it is an imitation of one.

• Reflection asks: “What can I learn from this? What will I do differently?” and ends in a conclusion.
• Rumination asks: “Why did this happen to me? Why am I like this?” and ends nowhere.

In the evening especially, when the day’s stimulation falls away, your brain slides into a setting that the neurologist Marcus Raichle named the default mode network in 2001.⁵ Put simply: the setting your brain switches to the moment it has nothing particular to do, and in which it starts thinking about you.

In people with depression, that setting is more strongly linked to a brain region involved in low mood, and it is precisely that link which predicts how much someone ruminates.⁶ This is where it gets subtler. That is an association, not a proven cause. Nobody knows whether the brooding creates the link, or the link creates the brooding.

The cost of not being here

In 2010, Harvard researchers Matthew Killingsworth and Daniel Gilbert published an astonishing result in Science. Through an iPhone app they asked 2,250 adults, at random moments: “What are you doing? What are you thinking about? How do you feel?”⁷

• On average, people are not present with what they’re doing for 46.9% of their waking hours.
• That absence does not follow unhappiness. It comes before it.

Their title was rawly honest: “A Wandering Mind Is an Unhappy Mind.” Even when your thoughts drift somewhere pleasant, you are less happy than when you are fully present with whatever you are doing. At the sink. Behind the wheel. At your child’s bedtime story.

An important nuance: letting go is not pushing away

Here this blog parts ways with the kind that says, “Smile and let it go!”

Not all looking back is rumination. Grief over what you have lost is not a problem to be solved. It is a process to be worked through. Trauma asks to be processed, not suppressed. The difference between grieving and ruminating is this: grieving gradually gives you more room, while rumination takes your room away.

If you are carrying something heavy, a loss, a betrayal, a wound that has not closed, then “just let it go” may be the most violent advice anyone can give you. Letting go is not turning off a tap. It is a slow homecoming.

I know how slow that homecoming is. After a hard divorce I knew, in my head, that I had to let go. I even knew it was unhealthy for me not to. And still it took years. Not because I was weak, but because letting go is not a decision you make on a Tuesday morning. Body, brain and heart walk that process at their own pace, not at the rhythm of what you know in your head.

What the research does show is this: noticing that you are in a ruminating loop is the first step out of it. Not by denying the pain, but by observing: “This isn’t reflection anymore. This is repetition.”

Ten small steps from yesterday to today

1. Name the loop. The moment you catch yourself telling the same story for the fifth time, say to yourself, “this is rumination.” Research by Matthew Lieberman and colleagues at UCLA shows that naming a feeling dampens activity in the amygdala, your brain’s alarm centre.⁸ The shorthand is name it to tame it.
2. Give rumination its own house. Schedule fifteen minutes of worry time a day, at a fixed moment and in a fixed place. Thomas Borkovec and colleagues described this technique back in 1983, and it has been one of the best-studied ways to rein in worry ever since.⁹
3. Write to release. The expressive writing research by James Pennebaker and colleagues shows that fifteen to twenty minutes of uncensored writing about a difficult experience brings measurable benefits for immune function and health.¹⁰
4. Set one anchor in today. Each morning, ask: “What is one thing I want to experience today, not achieve, experience?”
5. The five-senses pause. Name 5 things you see, 4 you hear, 3 you feel, 2 you smell, 1 you taste. Honestly: there is barely any research on this exact exercise. It pulls your attention outwards, and that is reason enough to try it. I promise nothing more with it.
6. Build closing rituals. A small physical act, washing your hands, hanging up your coat, closing a door, helps your brain switch between roles.
7. Be careful with social media after 9 p.m. Doomscrolling is rumination with a phone attached.
8. For every worried thought, ask: “Is this useful, or am I repeating?” Reflection has a conclusion. Rumination does not.
9. Move, but don’t expect too much of it. This point used to be stated too firmly here. A meta-analysis did find a benefit against rumination, but only for moderate-intensity aerobic exercise, once or twice a week, for five to eight weeks, in people with depression. It covered five studies and 260 participants, and the authors call their own finding preliminary.¹¹ One walk will not do it. In a study where a hundred people were randomly assigned to exercise or rest, those who exercised felt more positive afterwards, but did not ruminate any less.¹² Movement is good for you. It is not an off switch for your head.
10. Ask for help when it gets heavy. Letting go of trauma is not a solo feat. Calling in a professional is not weakness. It is the same wisdom that lets your dentist do the drilling instead of you doing it yourself.

In closing

This touches on my previous post: the difference between a fixed and a growth mindset. The fixed voice says, “I can’t do this. Today is too hard.” The growth voice says, “Today is hard and I’m more aware than I was yesterday.”

Letting go is not a leap. It is thousands of small steps, at your own pace, with the wisdom that it is allowed to take time. The past is over. And yet it lives on in you, in patterns, in the voice that says, “see, you were never meant to be able to do this.”

Today is not the absence of yesterday. Today is the place where you can give yesterday a new meaning, not by forgetting it, but by living in it less.

The gift of the present is not that it is painless. The gift is that it is yours.

Which story have you been telling yourself for years, and when did you last notice that you were repeating it?

This article provides general information and is not medical or psychological advice. If you have questions about your own health or wellbeing, please speak with your GP or a treating specialist.

Related reading

• Why Rest Has Become Unbearable
• The Desire Path in Your Mind
• Your Brain Is Not an Honest Witness

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Sources

The numbers in the text refer to this list.

1. Osborne, M., & Stevenson, J. (Directors). (2008). Kung Fu Panda [Film]. DreamWorks Animation.
2. Quote Investigator. (2023, July 26). Quote origin: The past is history. The future is a mystery. Today is a gift. That’s why it’s called the present. https://quoteinvestigator.com/2023/07/26/past-history/
3. LaFreniere, L. S., & Newman, M. G. (2020). Exposing worry’s deceit: Percentage of untrue worries in generalized anxiety disorder treatment. Behavior Therapy, 51(3), 413–423. https://doi.org/10.1016/j.beth.2019.07.003
4. Nolen-Hoeksema, S. (1991). Responses to depression and their effects on the duration of depressive episodes. Journal of Abnormal Psychology, 100(4), 569–582. https://doi.org/10.1037/0021-843X.100.4.569
5. Raichle, M. E., MacLeod, A. M., Snyder, A. Z., Powers, W. J., Gusnard, D. A., & Shulman, G. L. (2001). A default mode of brain function. PNAS, 98(2), 676–682. https://doi.org/10.1073/pnas.98.2.676
6. Hamilton, J. P., Farmer, M., Fogelman, P., & Gotlib, I. H. (2015). Depressive rumination, the default-mode network, and the dark matter of clinical neuroscience. Biological Psychiatry, 78(4), 224–230. https://doi.org/10.1016/j.biopsych.2015.02.020
7. Killingsworth, M. A., & Gilbert, D. T. (2010). A wandering mind is an unhappy mind. Science, 330(6006), 932. https://doi.org/10.1126/science.1192439
8. Lieberman, M. D., Eisenberger, N. I., Crockett, M. J., Tom, S. M., Pfeifer, J. H., & Way, B. M. (2007). Putting feelings into words: Affect labeling disrupts amygdala activity in response to affective stimuli. Psychological Science, 18(5), 421–428. https://doi.org/10.1111/j.1467-9280.2007.01916.x
9. Borkovec, T. D., Wilkinson, L., Folensbee, R., & Lerman, C. (1983). Stimulus control applications to the treatment of worry. Behaviour Research and Therapy, 21(3), 247–251. https://doi.org/10.1016/0005-7967(83)90206-1
10. Pennebaker, J. W., Kiecolt-Glaser, J. K., & Glaser, R. (1988). Disclosure of traumas and immune function: Health implications for psychotherapy. Journal of Consulting and Clinical Psychology, 56(2), 239–245. https://doi.org/10.1037/0022-006X.56.2.239
11. Li, S., Jia, J., Xu, B., & Wang, X. (2025). Effects of chronic exercise on different central features of depression in adults with depression: A systematic review and meta-analysis of random controlled trials. Psychology of Sport and Exercise, 78, Article 102824. https://doi.org/10.1016/j.psychsport.2025.102824
12. Schmitter, M., Vanderhasselt, M.-A., Spijker, J., Smits, J. A. J., & Vrijsen, J. N. (2023). Working it out: Can an acute exercise bout alleviate memory bias, rumination and negative mood? Cognitive Behaviour Therapy, 52(3), 232–245. https://doi.org/10.1080/16506073.2022.2164349

Sources on this site are cited in APA style, with a DOI wherever one exists. Why I made that choice →