Margen
You have two mental counters, and the 'today' one is rigged. When Richard Thaler put the same pair of prizes to Chicago students in 1981, 82% picked 100 dollars now over 110 dollars a month later. The same people, with both dates pushed away —100 dollars in a year or 110 in a year and a month— went for 110. The distance between the two dates is identical: thirty days.
The bias is called hyperbolic discounting. The 'today' counter sells you anything at an impossible discount: as if next week's self were another person who will foot the bill. It is what makes you sign the January gym subscription and cancel it in April. It is what makes you buy the extended warranty at the checkout and never claim it. It is what makes you eat the second croissant at eleven.
Three-step rule, fits on a note stuck to your wallet:
1. Before spending more than 50 euros you had not planned, write the choice pushed six months ahead: 'would I rather spend this on 15 February?'. 2. If you say yes, spend it today. If you say no, let 48 hours pass and look again. 3. Never decide at the card reader in a hurry: the hurry is the rigged counter.
The 'today' counter does not close. Move it somewhere else.