Your Brain’s Hidden Rules for Shaping Behavior
"To truly understand habits is to understand how the brain designs our behavior. Insight alone won’t magically change habits, but once you grasp why it’s so hard, you’ll know how to spend your time to earn better ones."
— Professor Jaeseung Jeong, from his recommendation of Hard To Break
With half of 2025 behind us, take an honest look at the goals you set earlier this year. Exercise, read more, sleep earlier, use your phone less, eat better… How many are still intact? For most of us, they fizzled out—or are stuck in the “I’ll restart tomorrow” loop.
We tend to blame ourselves: not enough willpower, too lazy, not persistent. But Stanford neuroscientist Russell Poldrack argues the opposite in his book Hard To Break: failed habit formation isn’t your fault—it’s how the brain is designed.
The brain was built to manufacture habits
According to Poldrack, the brain is a habit-making machine—for good evolutionary reasons. If you had to consciously think through every step of brushing your teeth (“squeeze the paste, put it on the brush, lift your hand…”) it would be exhausting. By automating repeated actions, the brain saves energy for more important problems.
The catch: this system doesn’t distinguish between good and bad habits. To your brain, checking your phone and going for a run are both “repeated patterns.” The behaviors that are more frequent and deliver immediate rewards win.
Brain imaging shows that during habitual behavior, prefrontal cortex activity (deliberate thinking) drops while the basal ganglia (automation) ramps up. Habits are “auto-programs”—which is why you can know the right thing and still not do it.
The truth about dopamine: not pleasure, but learning
Dopamine is often called the “pleasure chemical,” but that’s only half true. Work from Kent Berridge at the University of Michigan shows dopamine is really about expectation and learning.
At first, dopamine spikes at the reward (tasty food, a “like” notification). Over time, it shifts to the cue that predicts the reward (your phone’s buzz, the fridge hum): the essence of reward prediction error. Eventually, just picking up your phone triggers dopamine—and if the expected reward falls short, you feel let down. The brain has already wired “check phone ⇒ something good.”
In this process the brain performs chunking: binding a sequence of steps into one unit. Pick up phone → unlock → open app becomes a single automatic routine. Once chunked, the first step can trigger the entire sequence.
Habits aren’t erased—they’re overwritten
Here’s a crucial fact: once formed, habits aren’t scrubbed from the brain. Poldrack likens it to deleting a file—the traces remain on the drive. That’s why former smokers can relapse under stress or in old contexts: the old loop still exists and can be reactivated by the right cue.
Don’t despair. You can suppress old patterns by overwriting them with stronger new ones. Like walking a new path until the old trail grows over, repetition builds a circuit that outcompetes the previous one.
This isn’t about brute willpower—a limited resource that craters under stress and fatigue. Don’t lift the boulder; use a lever.
Five ways to build habits that match the brain’s algorithms
1. Redesign your environment
The most powerful (and most overlooked) lever is context. We are products of our environments, and the same person behaves differently in different settings.
To reduce a bad habit, increase friction: keep the phone out of the bedroom, remove tempting apps, turn off notifications. To build a good habit, decrease friction: lay out workout clothes, put your gym bag by the door.
Even stronger: place yourself in a new environment. Old contexts are packed with cues that trigger automatic loops. In fresh surroundings, the brain can’t find its old scripts, making deliberate choices easier. Try a new tool or new space for planning—your brain reads it as a “fresh start” thanks to context-dependent memory.
2. Remove choice with If–Then plans
Known as implementation intentions: “If situation A happens, then I do behavior B.”
Examples: “If I finish lunch, then I walk for 10 minutes.” “If I want social media, then I drink a glass of water first.” “If I feel angry, then I take three deep breaths.”
Pre-deciding creates automatic policies your brain can execute on cue—no in-the-moment debate required.
3. Write explicit rules to cut decision fatigue
We make thousands of decisions daily, each nibbling at willpower. Prevent evening backslides by codifying low-stakes choices:
- “No food delivery on weekdays.”
- “No work email after 6 p.m.”
- “No phone on weekend mornings.”
In places where smoking is categorically banned (hospitals, planes), the choice disappears—so the struggle does too. Clear rules do the same: red means stop, green means go.
4. Use monitoring and commitment devices
“What gets measured gets managed.” The brain is motivated by visible progress.
Start with a simple tracker: mark an X on days you exercise, an O when you read. Visual feedback taps the reward system, and streaks create a “don’t break the chain” effect.
Layer on commitments: tell a friend, “If I don’t read five books this month, dinner’s on me,” or pledge a donation if you miss. Because of loss aversion, these external stakes are potent.
5. Redirect old loops with substitute routines
Most habits are Cue → Routine → Reward. Keep the cue and reward, swap the routine.
If stress (cue) leads to sweets (routine) for relief (reward), replace it with a short walk (new routine) for the same relief (reward). You reuse the existing wiring while steering it to healthier behavior—far easier than inventing an entirely new loop.
A 3-Day Mini-Experiment: Rebuild your habit loop
Day 1 — Observe your current loops.
Watch yourself all day, especially the automatic moves. When do you grab your phone? In what situations do you snack? What emotions precede certain actions? Record without judgment.
Day 2 — Swap context + set If–Then.
Pick one habit to change. Add an environment switch (e.g., charge your phone outside the bedroom), and define one If–Then rule (“If I want to check my phone, then I read one page first”).
Day 3 — Build a simple monitor.
Create a quick checklist and log whether you executed the new behavior. Focus on attempts, not perfection. Instead of “Why did I fail?”, ask “How can I make the next attempt easier?”
The goal isn’t a perfect habit in three days; it’s insight into your patterns and the impact of small design tweaks.
The next 180 days: Design for how your brain works
Six months remain in 2025—plenty of time for new circuits. Studies suggest forming a new neural pathway often takes around 66 days on average, so you can sequence several habits across the rest of the year.
Don’t change everything at once. The brain treats abrupt overhaul as a threat and resists. Add one small habit per month. Once the first becomes semi-automatic, add the next.
Forget perfection. A habit you hit 80% of the time beats a flawless routine you abandon. Slips and regressions are normal. What matters is returning to the plan.
Habits aren’t will; they’re circuits. And circuits can be designed. Your brain is ready to change—use science to make it happen. Let the next six months be meaningfully different.