If you're anything like me, you can't get in and out of a supermarket without spending twice as much as you planned.
And you always leave with three or four things you don't really need and didn't go there to buy. Those incredible bargains at the ends of the aisle, delicious sweets at the checkout, the cooled fizzy drinks placed just at the exit or the most tantalising of treats at eyeing or grabbing height ...
An annoying, but random eventuality - or is it? ...
There is nothing random about the supermarket environment. The lack of windows, the generic streamlined layout, the long aisles - and even the bargains at their ends.
Supermarket layout is scientific - finely tuned and crafted to make you hungry, make you buy and even influence what you buy. I know this sounds like conspiracy theory, but this is the real deal.
The moment you walk in and grab your trolley, the experience has been purposely manipulated to guide your decisions in a direction that suits the supermarket and its big brands.
One. Quite the casino
Ever noticed you spend three times longer than planned at the supermarket?
Like casinos, supermarkets generally have no windows and therefore no natural light or reminders of the outside world. This is to limit our reference to the time of day and, with the bland, generic and streamlined interior, encourage us to stay longer and therefore buy more.
It's also been shown that brighter lighting may increase the chances of us picking up a product, and background music can increase the time we spend in a store. Spotlights at the ends of aisles increase the time we spend looking at the products under them.
Two. Chockies at the checkout
The Achilles heel of any shopper, those sweets and treats at the checkout are no accident either. Impulse shopping is well-studied and retailers know what products will sell - what brands, at what price and in what combination. Note the lack of home-brand options, let alone healthy alternatives.
High margin, high fat, high sugar and high salt - that is the recipe for the checkout.
Three. The science of placement
Based on eye-movement studies from as far back as the 1960s, products are placed on shelves at levels and stages in the aisles to maximise interest and boost sales.
Products which bring the largest profit margins - often the calorie-dense ones - are placed at eye level or between two shelves of "essentials" to ensure they're seen by shoppers.
Staples and perishable items have long been placed at the back of the store, as this ensures we must walk through the entire shop to get our daily milk and eggs ... passing the chocolate, cakes and ice-cream on the way.
Again, this is all based on solid evidences, not a store-manager's hunch.
What about those discounts at the ends of the aisles? They are chosen and stocked with precision.
Combinations of products are carefully paired and cases are filled to ensure that the products, while being discounted, don't appear cheap. Researchers also know that placing discounted cake mix next to cake icing, or crisps near soft drink, increases the sales of both. We go to buy one - or often none - realise it would be better with both and end up buying the pair.
Finally, aisle lengths are not random - studies have been done and the verdict is in. The longer the aisles, the more products one has to pass to get to what we want - and the more likely we are to buy more things. But too long, and we won't pass down them at all.
It's all a careful formula.
Eyes wide open
There is not necessarily anything wrong with the fact that supermarkets are being designed to increase consumption and manipulate buying habits. It is their space and their profit margins - but we had better be aware.
Science of selling
So next time you walk into the supermarket, reflect for a moment on what is placed where and how this influences your choices. Make active decisions on what you buy and stick to a list if you can.
Be under no illusions - the supermarket environment is a finely crafted science, and not a random collection of products. The supermarket chains know exactly what they're doing - and now you do, too.
• Alessandro R Demaio is an Australian medical doctor and a postdoctoral fellow in global health and non-communicable disease at Harvard University.