In this sense, (behavioural insights) BI offers proponents of (situational crime prevention) SCP a toolkit to better understand how decisions to commit a crime might be made. For example, behavioural science research suggests that people are typically bad at estimating risk, particularly when an individual’s own behaviour creates a risk to herself (smokers are often guilty of ‘optimism bias’, fully understanding the health risks of smoking yet rationalising that they can smoke while mitigating their own personal risks, see Arnett). This finding tallies with research on deterrence theory, which suggests that certainty of being caught is the most instrumental to behaviour change relative to other forms of deterrence, such as the celerity or severity of punishment (Nagin). An RCT exploring the mechanisms of Chicago’s Project Safe Neighbourhoods found that perception of risk was a common denominator in motivations to adhere to the programme (Trinkner). Similarly, part of the success of Hawaii’s high-intensity probation programme (Project HOPE) has been attributed to enhanced the perception of risk of punishment among probationers on the programme, with researchers finding that HOPE benefits from reputation effects that exceed the certainty delivered in practice (Hawken et al.).