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People add by default even when subtraction makes more sense

Picture a bridge made of legos. One side has three supporting pieces, the other two. How would you stabilize the bridge?

Most people would add a piece so that there are three brackets on each side, a new study suggests. But why not remove one piece so that each side has two supports? It turns out that getting people left out – whether it’s a block of Lego, ingredients in a recipe, or words in an essay – requires reminders and rewards, researchers report on April 7 in Nature.

This default value for addition is not limited to assembling blocks, cooking, and writing. Instead, thinking about advantages rather than disadvantages could contribute to current excesses such as cluttered homes, institutional administrative paperwork, and even an overloaded planet, says behavioral scientist Benjamin Converse of the University of Virginia in Charlottesville. "We're losing a whole class of solutions."

He and colleagues first observed the behavior when they asked 1,585 study participants to address eight puzzles and problems that could be solved by adding or removing some things. For example, a puzzle required shading or erasing squares in a grid to make a symmetrical pattern. In another, individuals could add or subtract items on a travel itinerary for an optimal experience. In all experiments, the vast majority of participants chose addition plus subtraction. For example, of 94 participants who completed the grid task, 73 squares added, 18 squares subtracted, and three others simply reworked the original number of squares.

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The researchers hypothesized that most participants did not add because they did not even think about the rest. Thus, through a series of controlled experiments, the team pushed participants toward the minus sign.

In one experiment, the team offered 197 people wandering around a crowded four-dollar university to solve a riddle. Participants saw a Lego structure in which was a figurine on top of a platform with a large pillar behind it. On that pillar, a single block in one corner supported a flat roof. The researchers asked participants to stabilize the roof to avoid crushing the figurine. About half of the participants were told, "Each piece you add costs 10 cents." Even with that financial sanction, only 40 out of 98 participants thought about removing the destabilizing block and simply supporting the roof over the wide pillar. The researchers gave a more explicit message to the remaining participants: "Each piece you add costs 10 cents but removing the pieces is free." That signal caused 60 of the 99 participants to remove the block.

tower of lego blocks with roofIn one experiment, participants had to stabilize a Lego roof over a figurine, represented by the piece of paper. Most people added pieces even though each piece cost 10 cents. Only when investigators specified that subtraction of parts was free did more people remove the destabilizing block and rest the roof on top of the wide pillar.Adams et al / Nature 2021

Practice helped participants remember that elusive minus sign, the researchers found. A variation in the grid experiment, where subtraction produced the top solution, showed that three practice races that led to the actual task resulted in more participants subtracting than those who solved the task without practice.

“When people try to do something better … they don’t think they can eliminate or subtract unless they are somehow instructed to,” says Gabrielle Adams, a behavioral scientist, also at the University of Virginia.

In contrast, bombarding participants with unrelated information decreased the likelihood of subtraction (SN: 24/05/20). People add even more when they experience an information overload, those experiments have shown.

At the intuitive level, people recognize that subtraction is less natural than addition, the authors say. Hence the adoption of sayings, such as “less is more” and Marie Kondo’s now infamous mantra to get rid of those things that fail to arouse joy.

But curbing our love of excess will take more than pushes and a clear mind, says Hal Arkes, a trial and decision-making researcher at Ohio State University who didn’t participate in the study. Organizational and political leaders, in particular, hate to cut fat. “If you add more people and more dollars, you won’t make any enemies, you’ll just make friends,” Arkes says. "Subtraction has serious disadvantages."

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