There's plenty of psychological research to show that when we spend using physical notes and coins, we spend more sensibly. Of all forms of payment, cash is the most "transparent" – the one that connects us most directly to the fact that we're parting with our money. That's also why, as the behavioural economist Dan Ariely has argued, cashlessness seems to be associated with increased dishonesty: it's easier to cut ethical corners involving money, while continuing to think of yourself as an honest person, when you're psychologically distanced from the money involved. "We are moving to a situation which allows people to rationalise dishonesty to a much, much higher degree," Ariely told Wired Magazine last year.