People are “too optimistic” that they can become regular gym goers and end up wasting a lot of money, according to a famous research paper cited in The Atlantic. The study found more people were more likely to sign up for a $70 a month gym contract than a $10 per visit package – despite only going to the gym four times a month. In behavioural economics terms, “hyperbolic discounting” can partly explain it, as we pay more attention to short-term well-being and put off exercise until “tomorrow”.

Three-for-two, limit 12 per customer – signs with numbers can influence how much shoppers buy, according to research cited on the Barking Up the Wrong Tree website. It says “almost any sign with a number promotion leads us to buy 30% to 100% more than we normally would”.

Buying experiences – such as travel or concert tickets – tends to boost happiness more than buying clothes, appliances or other objects, blogs academic and author Art Markman on Psychology Today. He writes that new research shows shoppers are much less likely to regret buying an experience. Of a big concert of a favourite band, Markman says: “You are more likely to regret passing up the opportunity to go to the concert than you are to regret buying a ticket to go.”