What drives human behaviour as consumers?

Three independent bodies of evidence, from psychology and behavioural economics, converge on the same answer: two distinct systems decide what people do next, not one.

Ask someone why they bought something and they'll give you a reason. Ask them why they picked their phone up for the fortieth time today and they'll struggle. That gap isn't a lapse in self-awareness. It's evidence of two separate systems running underneath almost everything people do: one built for speed, one built for judgement.

The split traces back to Daniel Kahneman's Thinking, Fast and Slow: System 1 is fast, automatic and runs with barely any sense of effort; System 2 is slow, deliberate and takes conscious work to engage. Behavioural science has since mapped two everyday categories onto that same split. Habit sits inside System 1 - the reach for the phone, the drive home on autopilot, the popcorn eaten without tasting it. Intent sits inside System 2 - booking the dentist, weighing a job offer, deciding to cancel something that isn't working.

The two operate differently enough that treating them as one thing, "what the consumer decided", misses most of what's actually happening. Wood & Rünger's 2016 review of the habit literature and Shotton's applied work in The Choice Factory both converge on the same distinctions, laid out below.

Trigger

Habit · System 1  A cue in the environment - sitting on the sofa, your hand is already reaching for your phone. Nobody decided that.

Intent · System 2  A decision - you notice a headache's been building all week and decide to book the dentist.

Processing

Habit · System 1  Automatic - you drive your usual route home without registering a single turn.

Intent · System 2  Deliberate - you sit down and actually weigh a new job: pay, commute, prospects.

Cognitive load

Habit · System 1  Low - you can brush your teeth while thinking about something else entirely.

Intent · System 2  High - you cannot do your tax return and hold a conversation at the same time.

Responsiveness to goals

Habit · System 1  Rigid - two weeks into a diet, you're still reaching for the biscuit tin at 3pm. The habit doesn't check in with the goal.

Intent · System 2  Adaptive - you cancel a restaurant the moment you read one bad review.

Sensitivity to outcome

Habit · System 1  Low - the behaviour persists even once it stops paying off (see the popcorn study below).

Intent · System 2  High - you cancel a gym membership the moment it stops paying off.

Self-awareness

Habit · System 1  After the fact - you snap at someone and only realise afterwards that you were just hungry.

Intent · System 2  In the act - you draft the angry email and consciously decide to sleep on it first.

The clearest evidence for how differently the two systems treat outcomes comes from an experiment on cinema popcorn. Neal, Wood, Wu and Kurlander gave moviegoers with a strong habit of eating popcorn at the cinema either fresh or stale popcorn, then watched what happened both inside the cinema and in a plain meeting room.

Inside the cinema, habitual eaters got through roughly as much stale popcorn as fresh - the cue (the seat, the dark, the film) was doing the driving, not the taste. Move the same people to a meeting room, away from the cue, and the habit lost its grip: even strong habitual eaters ate noticeably less stale popcorn once the automatic trigger was gone. Get people to eat with their non-dominant hand, disrupting the motor pattern, and the same thing happened - consumption of stale popcorn dropped as soon as eating stopped being automatic.

That's what Wood & Rünger mean when they describe habits as insensitive to outcomes: the behaviour doesn't recalculate each time based on whether it's still worth it. Intent does. It's why someone will drop a gym membership the moment it stops paying off, but keep buying the same snack out of habit long after they've stopped particularly wanting it.

The self-awareness dimension is the one with the most consequence for marketers. Habit runs quietly, in the background, most of the day. Intent is the bit people actually notice themselves doing, which is exactly why they - and the brands trying to reach them - overrate how much control it has.

Habit runs quietly, in the background, all day. Intent is the bit we actually notice ourselves doing - which is why we overrate how much control it has.

That asymmetry cuts to something advertisers have to sit with: most everyday buying behaviour is running on System 1, cue-triggered and largely unreported, while most of the measurement built to understand it, surveys, stated preference, declared purchase intent, is built for System 2. It asks people to narrate a decision that, more often than not, they never consciously made.

Sources

Kahneman, D. (2011). Thinking, Fast and Slow. Penguin.

Wood, W., & Rünger, D. (2016). "Psychology of Habit." Annual Review of Psychology, 67, 289-314.

Neal, D. T., Wood, W., Wu, M., & Kurlander, D. (2011). "The Pull of the Past: When Do Habits Persist Despite Conflict with Motives?" Personality and Social Psychology Bulletin, 37(11), 1428-1437.

Shotton, R. (2018). The Choice Factory: 25 Behavioural Biases That Influence What We Buy. Harriman House.