Behavioural design

System 1 and 2

In his book 'Thinking, fast and slow', Daniel Kahneman explains that everyone has two modes of thinking: system 1 and system 2.

System 1 is the fast, instinctual part that's sometimes called our 'reptile brain'. It makes rapid automatic decisions that sometimes aren't the best choices, but use smaller amounts of cognitive resources.

System 2 is more rational (thought not completely rational), but this comes at the cost of speed and energy. System 2 is much slower and requires more cognitive resources.

While we imagine we do most of our thinking using system 2, we actually use system 1 for most of the time.

Implications for research

System 2 doesn't really understand why system 1 does what it does. That means it can't accurately predict what system 1 would do in future, or explain why system 1 did something in the past.

In most research contexts, the research subjects will be using system 2 to think carefully about questions and answer them correctly. Unfortunately, when they're in the real world actually doing the things they're talking about, they'll be using system 1.

To get around these limitation, you need to:

  • conduct research in an environment as close to reality as possible. This includes things like physical location, noise levels, time of day, and mental states (if your user would normally be multitasking, get them to multitask during testing).
  • measure real behaviour where-ever possible, by releasing smaller things earlier on, then iterating

Ulysses Pacts

A Ulysses Pact is where system 2 does something ahead of time which constrains how system 1 can behave in the moment.

For instance, not buying unhealthy snack food means that you can eat biscuits when you get bored.

There are some successful products that use this model. 

Focus is a Mac app that blocks distracting sites/apps for set periods.

Pact asks you to commit to doing/not doing certain things, and pledge some money. If you keep to your commitments, you keep the money but, if you slip up, you lose some of the money.


Thinking, Fast and Slow, by Daniel Kahneman