Every behavior has an origin. Most people never identify it.
You opened your phone 96 times yesterday. Some of those times, something in the world demanded it — a notification sound, a colleague saying "check Slack," a calendar alert. But most of those times, nothing external happened at all. A feeling arose — boredom, curiosity, low-grade anxiety — and your thumb was on the screen before you consciously decided anything.
This is the fundamental distinction in trigger design: internal triggers originate inside you (emotions, thoughts, physical sensations), and external triggers originate in your environment (sounds, notifications, visual cues, events, other people's actions). The distinction matters because the redesign strategy for each category is completely different. You fix external triggers by changing your environment. You fix internal triggers by changing your relationship to your own signals.
Most people only see external triggers because external triggers are observable. Internal triggers are invisible — even to the person experiencing them. And that invisibility is precisely what makes them powerful.
Internal triggers: your body and mind as signal generators
An internal trigger is any thought, emotion, or physical sensation that initiates a behavior. You feel anxious, so you check email. You feel lonely, so you open Instagram. You feel a dip in energy, so you reach for sugar. No one told you to do any of this. No alarm went off. The signal came from inside.
Nir Eyal, in Hooked: How to Build Habit-Forming Products (2014), identified internal triggers as the engine of sustained habit formation. His Hook Model describes a four-phase cycle — trigger, action, variable reward, investment — and the critical insight is that while a product may initially rely on external triggers (ads, notifications, onboarding emails) to get a user through the first few cycles, long-term engagement depends on the product becoming associated with an internal trigger. The product becomes the default response to a recurring emotional state. Facebook didn't succeed because of push notifications. It succeeded because loneliness, boredom, and the fear of missing out became automatic cues to open the app. The external trigger was the on-ramp. The internal trigger was the engine.
Internal triggers fall into three categories:
Emotional triggers. These are the most studied and the most powerful. Anxiety, boredom, loneliness, frustration, shame, excitement — each of these emotional states has a characteristic behavioral signature. You don't decide to respond to anxiety by checking your inbox. The pairing has been reinforced so many times that the emotion fires the behavior directly, bypassing deliberation. Charles Duhigg's habit loop research, published in The Power of Habit (2012), showed that the cue in a habit loop can be an emotional state just as readily as a time of day or a location. The Golden Rule of habit change — keep the cue, replace the routine, keep the reward — works the same way whether the cue is "3 PM" or "I feel restless."
Somatic triggers. These are physical sensations in your body: a tight chest, a churning stomach, muscle tension, hunger pangs, fatigue, a racing heart. Antonio Damasio's somatic marker hypothesis proposed that emotional decision-making is fundamentally rooted in body states — the brain reads physiological signals and uses them to bias choices toward or away from particular actions. Your "gut feeling" about a decision is not a metaphor. It is a literal interoceptive signal — information from your viscera being processed by the ventromedial prefrontal cortex and translated into an action tendency. A tight stomach before a difficult conversation is a somatic trigger that, left unexamined, might cause you to avoid the conversation entirely.
Cognitive triggers. These are thoughts and mental patterns that initiate behavior: rumination, comparison, self-criticism, planning spirals, "what if" thinking. You think "I should really check on that deployment" and find yourself in the monitoring dashboard without having made a deliberate choice. The thought was the trigger. Cognitive triggers are particularly insidious because they masquerade as rational decision-making — "I had a reason to do that" — when the actual mechanism was an automatic thought-to-action chain.
The science of reading your own signals
The ability to detect internal triggers depends on a capacity called interoception — your brain's ability to sense and interpret signals from inside your body. Lisa Feldman Barrett's theory of constructed emotion, published in Social Cognitive and Affective Neuroscience (2017), reframed emotions entirely around interoception. In Barrett's model, the brain continuously generates predictions about the body's internal state — what she calls "body budgeting" — and emotions are the brain's interpretation of those predictions within a given context. You don't feel anxious and then your heart races. Your heart races, your brain predicts "this pattern plus this context means danger," and the resulting construction is what you experience as anxiety.
This has direct implications for trigger design. If emotions are constructed from interoceptive signals, then improving your interoceptive accuracy — your ability to correctly sense and interpret what is happening inside your body — improves your ability to detect internal triggers before they fire automatic behaviors. A 2025 study in Frontiers in Neuroscience found that interoceptive sensibility modulates risk-taking behavior: people with better body-signal awareness made more calibrated decisions under uncertainty, presumably because they could read their somatic state more accurately and use it as information rather than being controlled by it.
The practical takeaway: you cannot redesign internal triggers you cannot detect. And detection is a skill that improves with practice. Mindfulness, body scanning, and even basic journaling ("what was I feeling right before I did that?") all improve interoceptive accuracy over time.
External triggers: the environment as signal generator
An external trigger is any stimulus in your environment that initiates a behavior. These are visible, auditable, and usually designable:
Notifications and alerts. The most obvious category. Your phone buzzes, you respond. A badge count appears, you tap it. An email arrives, you read it. Tech companies have optimized external triggers to a science — variable timing, social proof ("3 people liked your post"), and urgency signals ("limited time") are all engineered external triggers designed to capture your attention.
Environmental cues. A sticky note on your monitor that says "breathe." The gym bag you placed by the front door. The book on your nightstand. A clean desk versus a cluttered one. BJ Fogg's Behavior Model, developed at Stanford's Behavior Design Lab, emphasizes that behavior occurs when motivation, ability, and a prompt converge at the same moment. Fogg originally called the third element a "trigger" before renaming it a "prompt" in 2017. External prompts are the most designable element: you can literally place them in your environment where and when you want the behavior to occur.
Time-based cues. Your alarm goes off. It's noon, so you eat lunch. The calendar says "stand-up meeting." Time-based triggers are external even though they feel automatic — the clock is in the environment, and the behavior is conditioned to fire when the time arrives.
Social cues. Someone asks you a question, you answer. A colleague starts packing up, you start packing up. Your team switches to Slack, you switch to Slack. Social triggers are among the most powerful external cues because humans are deeply wired for social responsiveness, and they operate even when you are not consciously tracking what other people are doing.
Event-based cues. You finish one task and that completion triggers the next. The build passes, so you deploy. The meeting ends, so you write up notes. Event-based triggers chain behaviors together — the output of one process becomes the input signal for the next.
The asymmetry: why internal triggers dominate
Here is the pattern most people miss: external triggers get most of the attention because they are visible, but internal triggers drive most of the behavior. Eyal makes this point explicit — the goal of every habit-forming product is to graduate from external triggers to internal ones, because internal triggers are self-sustaining. An external trigger requires the environment to be configured correctly every time. An internal trigger fires whenever the emotional state recurs, which for states like boredom and anxiety means dozens of times per day.
This asymmetry explains why environment design alone is not sufficient for behavior change. You can turn off all notifications, clear your desk, delete social media apps from your phone — and still find yourself procrastinating, because the internal trigger (anxiety about the hard task) is still firing and finding some other behavior to attach to. The anxiety doesn't disappear because you removed Instagram. It finds another outlet.
Conversely, this asymmetry also explains why understanding internal triggers is the highest-leverage skill in trigger design. If you can learn to notice the emotional state before it fires the automatic behavior, you gain a choice point — a moment where you can redirect the energy toward a behavior you actually want.
The AI parallel: user-initiated versus system-initiated events
If you build or work with software systems, this distinction maps cleanly to event-driven architecture. A user-initiated event is triggered by a human action — a button click, a form submission, a voice command. The system responds to an input it received from outside. A system-initiated event is triggered by the system's own internal state — a cron job, a threshold being crossed, a health check failing, a machine learning model detecting an anomaly.
The parallel is precise. User-initiated events are external triggers: the environment sends a signal, the system responds. System-initiated events are internal triggers: the system monitors its own state and initiates behavior when internal conditions are met.
And the same asymmetry holds. Junior engineers tend to build systems that only respond to external events — user clicks, API calls, webhook payloads. Mature architectures also monitor internal state: memory pressure, queue depth, model drift, error rate trends. The system that only reacts to external events is fragile in the same way a person who only responds to notifications is fragile — it has no capacity for self-initiated behavior based on internal conditions.
Designing yourself as a well-architected system means building both channels: external triggers you can place in your environment, and internal triggers you can detect, classify, and route to the behaviors you actually want.
Designing for both channels
The reason this distinction matters is that the redesign strategy differs by trigger type:
For unwanted behaviors driven by external triggers: Remove or modify the environmental cue. Turn off the notification. Move the candy jar off your desk. Block the website during work hours. This is environment design, and it works — but only for the external channel.
For unwanted behaviors driven by internal triggers: You cannot remove the cue because the cue is your own emotional or somatic state. Instead, you have three options: (1) improve detection, so you notice the trigger before the automatic behavior fires; (2) reroute the trigger, so the same emotional state activates a different, preferred behavior; or (3) address the underlying state directly, so the trigger fires less frequently. Option 1 is interoceptive training. Option 2 is Duhigg's Golden Rule. Option 3 is therapy, sleep, exercise, and the other interventions that regulate baseline emotional volatility.
For desired behaviors you want to make automatic: Use external triggers initially — place the cue in your environment, set the alarm, ask someone to remind you. Over time, pair the behavior with an internal state so it becomes self-triggering. This is exactly Eyal's Hook Model applied to your own behavior rather than a product: start with the external prompt, build the association, and eventually the internal trigger sustains the behavior on its own.
The next lesson addresses what makes a trigger reliable. But reliability starts here, with correctly identifying which channel the trigger operates in. An external fix applied to an internal trigger will always fail. An internal fix applied to an external trigger is unnecessary overhead. Classification precedes design.
Sources:
- Eyal, N. (2014). Hooked: How to Build Habit-Forming Products. Portfolio/Penguin.
- Duhigg, C. (2012). The Power of Habit: Why We Do What We Do in Life and Business. Random House.
- Fogg, B.J. (2009). "A Behavior Model for Persuasive Design." Stanford Behavior Design Lab. behaviormodel.org
- Barrett, L.F. (2017). "The theory of constructed emotion: an active inference account of interoception and categorization." Social Cognitive and Affective Neuroscience, 12(1), 1-23.
- Damasio, A.R. (1996). "The somatic marker hypothesis and the possible functions of the prefrontal cortex." Philosophical Transactions of the Royal Society B, 351(1346), 1413-1420.
- Garfinkel, S.N., Seth, A.K., Barrett, A.B., Suzuki, K., & Critchley, H.D. (2015). "Knowing your own heart: Distinguishing interoceptive accuracy from interoceptive awareness." Biological Psychology, 104, 65-74.
- Cowan, N. (2001). "The magical number 4 in short-term memory." Behavioral and Brain Sciences, 24(1), 87-114.