What is Sunk Cost Bias and how is it affecting your spending decisions?


As business owners, we’d like to think that we make rational, logical decisions regarding our business finances. However, scientists have discovered hardwired biases in our minds and thought processes, one of which is the sunk cost bias, also known as sunk cost fallacy.


A sunk cost is simply money, time, or resources you have already spent and can’t recuperate. Another word for them is retrospective costs. The bias comes into the picture when we consider those costs in future decisions.


The sunk cost fallacy, first hypothesized by Richard Thaler in 1980, is a cognitive bias where people overestimate the importance of sunk costs in their decision-making. He wrote, “Paying for the right to use a good or service will increase the rate at which the good will be utilized.”


In a 1985 paper by Hal Richard Arkes and Catherine Blumer titled “The Psychology of Sunk Cost,” the authors found evidence that this tendency is “predicated on the desire not to appear wasteful.” Furthermore, “those who had incurred a sunk cost inflated their estimate of how likely a project was to succeed compared to the estimates of the same project by those who had not incurred a sunk cost.”


Essentially, instead of making a decision that’s right for themselves and their future based on current circumstances, people will make a decision heavily informed by the action already taken, even when it isn’t relevant to current circumstances. It doesn’t sound very productive, does it?


Let’s discuss two examples of the bias in action. First, let’s say you have spent a lot on car repairs. You continue to repair the car, digging a deeper and deeper hole. Making a $3,000 downpayment toward purchasing another vehicle is likely a better decision than sinking the same amount of money into another round of repairs. However, you are still emotionally (and irrationally) attached to all the money you spent on the clunker.


Now say you have an employee that is a borderline performer. You keep investing in them, thinking you can “fix” them. However, they don’t improve. Regardless of whether the employee is insubordinate or simply not the right fit for the role, letting them go was likely the right move to make some time ago. 


So, now that you know about the sunk cost bias, how can you avoid falling into it in your business? Here are some ideas:


  1. Increase your mindfulness when making decisions that involve costs already incurred. Ask yourself, “what decision would I be making if I hadn’t already invested the time/money/resources into this project?”
  2. Since the bias can often come as the result of not wanting to experience negative emotions like feelings of failure, irresponsibility, or loss, try to remove your emotions from the equation altogether. Instead, examine the business project at hand from a facts-only perspective. Ask yourself, “What does the data show me?” Then do the math. 
  3. Track key performance indicators (KPIs) regularly to see whether you’re on or off track and assess whether it’s worth continuing the project sooner.
  4. Like setting a budget for holiday shopping, establish goals and milestones for future projects, and have a “walk away” plan if things spiral out of control.
  5. Stay future-focused.


Ultimately, it will be up to you to ensure that sunk cost bias doesn’t affect your decision-making in the future. Hopefully, this information and the five tips we provided will help you orient yourself to make business decisions that benefit current and future you, rather than past you.


If you’d like to learn more about cognitive bias, including the sunk cost bias, check out the works of two additional scientists, Daniel Kahnerman and Amos Tversky (the former of whom won the Nobel prize for his work!).

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