What sends you to the shop
If the want didn't come from the bag, it came from somewhere. The research points to your mood.
In 2008 Cynthia Cryder and three colleagues ran a small experiment that has become well known. Thirty-three people watched a film clip. Some saw a sad scene about a boy whose mentor dies, and the others saw a neutral one. Then, in what they were told was a separate task, each was offered the chance to buy an insulated water bottle, naming the most they'd pay out of their ten-dollar fee. The people who'd watched the neutral clip offered an average of 56 cents. The people who'd watched the sad one offered $2.11. It was the same bottle, and it was worth nearly four times as much to someone who'd just been made sad.
Two details matter. The effect appeared only in people whose sadness had turned their attention onto themselves. And a later study by Nitika Garg, Lisa Williams and Jennifer Lerner, which repeated the finding in a new setting, confirmed that it happens even when people are unaware of it. Nobody in these studies thought, I'm sad, so I'll pay more for a bottle. They thought the bottle was worth two dollars.
That's the important bit. A low mood doesn't announce itself as a reason to shop. It works by making things look more worth having, so from the inside all you notice is a nice bag.
Outside the laboratory the same link shows up at scale. Mark Fenton-O'Creevy, Sally Dibb and Adrian Furnham analysed a UK survey of more than a hundred thousand people. Impulsive buying was more common in those with the most need to manage their moods and the fewest good ways of doing it. It also went with worse financial outcomes, and not only among the heaviest buyers. And in Black's review of compulsive buying, the feelings that patients most often named as coming before a spree were depression, anxiety, boredom, self-critical thoughts and anger.
You've probably been told not to go to the supermarket hungry. The hunger fills the trolley, and the person who unpacks it at home isn't hungry any more and wonders who chose all this. A flat mood does the same job on a shopping site, except that nobody warns you about it.
This is where the title of the book comes from. If a want is produced by the state you're in tonight, then it has no history. It wasn't there yesterday. A want that comes from your life and not your mood usually does have a history. You've noticed the lack before, more than once, on good days as well as bad. So there's a question that sorts the two well enough.
Did I want this yesterday?
It isn't proof. Now and then you'll see something for the first time that you need, and the answer will be no. But in that case nothing is lost by waiting, because a real need will still be there on Friday. A want that was made by Tuesday evening mostly won't outlast Tuesday evening. The question never tells you not to buy it. At most it tells you to hold off for tonight.
You can also turn the question round, and it's worth doing once. When the urge to browse arrives, ask what happened today. Most evenings you'll find an answer quickly. Something went wrong, or nothing went right, or the day was blank. That answer is what you were shopping for.