The Three Laws of Human Behavior
The Basic Idea
If you took physics in high school, you’re familiar with Newton’s three laws of motion. These rules describe the relationship between the motion of a body and the forces acting on it, and were first proposed in the 17th century by English mathematician Isaac Newton.¹ Remarkably, Newton managed to distill complex and difficult physical concepts into three simple, universal rules.
The three laws of motion are:
- A body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by an external force.
- The force acting on an object is equal to the mass of that object times its acceleration.
- For every action, there is an equal and opposite reaction.
Until Newtonian physics was displayed by quantum mechanics and general relativity in the early 20th century, these laws were thought to describe how all objects and their motion are impacted by forces. They are still used frequently in calculations and do reflect the motion of objects accurately — unless we are talking about quantum particles or extremely massive bodies. But can we apply these laws to anything else? In a 2019 article for Behavioral Economics, Aline Holzwarth, a behavioral scientist, used Newton’s laws of motion to inform three laws of human behavior.²
These three laws are:
- Behavior tends to follow the status quo unless it is acted upon by a decrease in friction or increase in fuel.
- Behavior (B) is a function of the person (P) and their environment (E), or B=f(P,E).
- For every decision made, there are tradeoffs and the potential for unintended consequences.
Although human behavior is complicated, Holzwarth suggested that these laws can at least capture very general behavioral tendencies.
Other social scientists have compared psychological and sociological tendencies to the universal laws of physics, but Holzwarth is responsible for drawing three clear laws from Newton’s laws.3 Like the laws of motion, Holzwarth’s three laws of human behavior set out to describe behavior at large and can break down in specific instances. Although Newton’s theories were ultimately replaced by quantum mechanics and relativity, the three laws of motion continue to be helpful outside of bodies of mass that are either extremely large or small. Similarly, the laws of human behavior could be most powerful when used as approximations of general tendencies.
The first law says that behavior tends to follow the status quo unless it is acted upon by a decrease in friction or increase in fuel. Holzwarth summarises this law in a concept we are all probably familiar with: humans tend to take the path of least resistance. When we let our “autopilot” take control of our decisions, like making a healthy meal versus ordering in, our automatic response will be to choose the most convenient option — even if it is a poor choice in the long run. This behavior is captured by the Status Quo Bias, which describes our preference to continue what we are doing. Even if it makes sense to make a change, like walking to work instead of driving to get more exercise, we are naturally resistant to switching up our routine.
Similar to inertia in Newton’s first law of motion, the status quo bias stands in the way of changing our behavior. We need a certain amount of force for a change to take place. Indeed, inertia has actually been defined in behavioral science due to our resistance to change. Holzwarth describes two primary kinds of forces that determine human behavior: friction and fuel. Friction is a negative force because it acts as an obstacle to performing a behavior. For example, friction can be the phone call we need to make to make a doctor’s appointment, or the line we have to stand in to renew our driver’s license.
This means that changing our behavior is often quite hard, unless the other primary force, fuel, can overpower the friction in a situation. Fuel makes behaviors more appealing, like social and monetary rewards for completing certain tasks (i.e. going to work). Whether or not we can change our behavior depends on the balance of fuel and friction.
The second law of human behavior, analogous to the law behind the famous F = ma relationship in physics, suggests that behavior (B) is a function of the person (P) and their environment (E), or B=f(P,E). Holzwarth explains that behavior depends on the particular person and their personal values, beliefs, experiences, etc., along with the specific environment the person finds themself in. This includes the physical environment, sensory elements, their social circle, and any other external factors. One clear example of the influence of our environment on behavior is in-store displays and layouts, like the candy and small snacks located in the check-out aisle of a store. While customers are waiting, they may be tempted to pick up a chocolate bar since it is in front of them, even if their personal factors (hunger, health conscientiousness) are not particularly in favor of buying one.
The equation B=f(P,E) is not Holzwarth’s creation, but goes back to one of the pioneers of modern social psychology, Kurt Lewin. He first proposed this universal relationship in 1936, emphasizing the importance of the interaction between a person and their environment in determining their behavior.⁴ Holzwarth also emphasizes that in B=f(P,E), behavior is determined not by the person and environment in isolation from each other, but by how the person reacts to their environment. Although we have the tendency to underestimate the influence of situational factors on a person’s behavior due to a bias called the fundamental attribution error, the second law of human behavior serves as a reminder that we need to understand both the person, the environment, and their interaction to explain behavior.
The third law (based on the concept that when two bodies interact they apply forces to one another that are equal in magnitude and opposite in direction) is that for every decision made, there are tradeoffs and the potential for unintended consequences. This may be the most general and seemingly obvious of the laws, but Holzwarth argues that we often do not consider the tradeoffs and unintended consequences of our decisions. For example, with the traditional pros and cons approach to decision-making, we can overlook the opportunities we lose by choosing a particular option, also known as the opportunity cost. If we decide to buy a healthy salad for lunch everyday at work, we lose the opportunity to spend that money on other health-related foods or treatments.
Another part of decision-making that we often overlook are unintended consequences. These are the results we do not see coming, whether they affect us or not. On a global scale, harmful ecological effects are common unintended consequences of behaviors. Even well-intentioned social movements can have unexpected negative impacts on the cause they are trying to address. For instance, consider the consequences of a plastic straw ban. It seems like a clear solution to reduce plastic waste and negative environmental effects. Yet, banning plastic straws removes the weight of making an environmentally-friendly decision off of the consumer, thereby taking away the mental effect of customers consciously considering their impact on the environment. As a trickle-down effect, consumers may be less thoughtful of the environmental effect of their other choices, and will not internalize the environmental message behind the popular movements which drove the bans in the first place.
These laws provide a very basic and broad framework with which to understand our behavior and that of those around us. Holzwarth incorporates a number of well-established biases and heuristics underneath her three main laws, effectively capturing many important concepts in behavioral science. As Holzwarth notes is her intention, the laws do not present anything new but instead consolidate a multitude of ideas in the field into these general rules. For the average person, these may be a more friendly reminder of our tendencies than a long list of individual biases.
In this way, the laws act similarly to their analogues in physics — they distill a field of complex theories into three simple laws. Holzwarth’s aim is that the laws of behavioral science can inform how we design products. Just as Newton’s laws continued to be used for calculations and understanding the motion of most objects, these laws can hopefully serve as a tool to form products and services based on our behavior. Even if there are specific instances where these laws no longer hold true, as is the case when Newton’s laws are applied to quantum particles or extremely massive objects, these generalizations can nevertheless lead us to better apps and programs.
Laws in behavioral science have to be very general as a rule, and even so, human behaviors can always fall outside a specific law — unlike how we expect physical matter to adhere to certain laws. As psychology is considered a “soft” science, the field is generally averse to theorizing fundamental rules that govern behavior. Moreover, it may seem a little forced to try to translate Newton’s laws of motion into similar laws for human behavior. That said, the laws do feel intuitive once Holzwarth explains them, and like Newton’s laws, appear to be obvious even if we were not able to form the connections before reading about them.
Other questions Holzwarth addresses are: why create these laws now? Are they really that helpful? Holzwarth suggests that behavioral science as a field is currently undergoing a parallel change to the transformation of physics during Newton’s time. Advances were happening rapidly, fuelled by the demand for industrial applications from physics. Similarly, Holzwarth argues, there is currently a serious necessity for innovative and competitive companies to incorporate behavioral science insights not only for marketing and management purposes, but for domains such as product development, healthcare, and banking. As a result, there is a need for behavioral scientists to communicate and organize their work in a way that others can understand and apply to their own respective fields. These laws serve as an effective guide for generalized human behavior, and incorporate many well-established theories, biases and heuristics within them.
In the same way that Newton’s theory of gravity and laws were overturned in the 20th century by quantum mechanics and relativity but still continue to be used as helpful tools for approximate calculations, the three laws of human behavior have the greatest potential as a guide for professionals both familiar and unfamiliar with behavioral science to develop better products. Human behavior is known to be complex and varied, but it nevertheless often follows certain rules, just like physics. These generalizations can help us understand our own behavior at least in part and even more so help us understand the behavior of those around us.
Related TDL Content
The Status Quo Bias describes our resistance to change, or our preference for the current state of affairs. This bias frees up our mental resources for other tasks, but small decisions we relegate to our “auto-pilot” can fall prey to the status quo bias over and over, resulting in little change even when we do want it. Read more about the status quo bias in our reference guide.
Inertia refers to an object’s tendency to resist a change in motion. As the first law of human behavior suggests, people also resist change and prefer to stick with the status quo. As a result, behavioral scientists have studied inertia in terms of our tendency to continue interpreting information the same way. This reference guide entry describes the history of inertia as a behavioral science concept, and how we can apply this physical idea to how cognition works.
This article explores the power and frequent irrationality of our resistance to change. Often, regardless of how we feel about a choice, we will avoid making a change, as the first law of human behavior describes. No matter how attractive a behavior is, if the friction blocking the behavior is stronger than the fuel, we will resist change.
This bias occurs when we make judgements about another person’s behavior and disproportionately attribute their actions to their personality more than situational factors. As the second law of human behavior indicates, a person’s behavior is determined by the interaction between a person and their environment. Both personal and situational factors are important, and critically, a person’s unique reaction to their surroundings will determine their behavior.
In this article about the pros and cons of plastic straw bans, Holzwarth’s third law is on full display. Although banning straws would clearly reduce plastic waste, the opportunity cost means that consumers lose the opportunity to make conscientious decisions about their environmental impact. This can also be seen as an unintended consequence, where bans essentially make the choice for the consumer, meaning that they are less encouraged to think about their environmental impact in other situations.
- Encyclopaedia Brittanica. (2021, July 23). Newton’s Laws of Motion. In Encyclopaedia Brittanica. https://www.britannica.com/science/Newtons-laws-of-motion
- Holzwarth, A. (2019, May 7). The Three Laws of Human behavior. Behavioral Economics. https://www.behavioraleconomics.com/the-three-laws-of-human-behavior/
- Mousavi, S., & Sunder, S. (2019). Physical Laws and Human Behavior: A Three-Tier Framework. 10.31219/osf.io/nmpc8.
- Encyclopaedia Brittanica. (2021, September 5). Kurt Lewin. In Encyclopedia Britannica. https://www.britannica.com/biography/Kurt-Lewin