When we go to a supermarket, we often buy more than we need. But it may not be our fault—supermarkets are controlling the way we shop. In fact, the whole experience of shopping for food is planned so that we stay longer and spend more. [A]

From the moment we enter, we are controlled by a supermarket’s floor plan. The first thing we usually see at the entrance is an attractive space full of colorful fruit and fresh vegetables. This part of the floor plan makes us feel good so we look forward to our time in the supermarket. It also slows us down—stopping us from quickly getting the items on our shopping list. [B]

The floor plan is also designed to make us pass through as much of the store as possible. Supermarkets put items that most people buy—such as milk and eggs—at the back of the store. This forces us to walk through several aisles. Cash registers are usually near the exit, so we have to walk back through more aisles. Supermarkets hope that during this long journey, we will see—and buy—more items than we were planning to. [C]

The more time we spend in a supermarket, the more money a supermarket makes. Studies show that after about 30 minutes, we stop shopping rationally. Instead, we shop emotionally. We start to add items to our cart because it makes us feel good, not because we planned to buy the item. This is when we buy extra items—items that are not on our shopping list. [D]

Supermarkets also have strategies to make us buy more expensive items. When we are in an aisle, we usually look at the shelves from top to bottom—the same way we read a book. So supermarkets put expensive items at eye level because we see those items first. They are also easy to reach. Cheaper items are on lower shelves, so we have to bend down to get them. This makes us more likely to grab the more expensive items. [E]

Supermarkets can use music to control our shopping, too. In a study of shopping habits in a New York City supermarket, researchers found that playing slow music in a store made shoppers walk more slowly. This meant they spent more time—and money—in the store. In fact, on days when the supermarket played slow music instead of fast music, shoppers spent about 38 percent more. [F]

So, how can you avoid buying more than you need? The best advice is to make a list, and don’t buy anything that isn’t on it. Or perhaps try ordering from the supermarket online. [G]

The paths in a supermarket that customers walk down and that separate the shelves of food are aisles.

If you do something rationally, you do it with clear thinking.