A sunk cost is money, time, effort, or any other resource that has already been spent and cannot be recovered.
At first glance, the idea seems simple. If a resource has already been spent, it should not influence our next decision. But in real life, people often do the opposite: they continue an unsuccessful project, remain in unsuitable relationships, hold on to a useless purchase, or spend even more time simply because they have already invested too much.
This is precisely what is called the sunk cost fallacy.
Consider a simple example. You bought a cinema ticket for 20 euros. Half an hour into the film, you realize that you do not like it at all. You cannot get the ticket money back. The rational question should be: “Do I want to spend another hour and a half watching this film?” But people often think differently: “I already paid 20 euros, so I have to watch it to the end.”
In reality, those 20 euros are already lost regardless of whether you stay in the cinema or leave. The only resource you can still decide how to use is your remaining time.
The same logic applies to more serious situations.
A person may stay for years in a job that does not suit them because they have already built a career in that field. They may continue investing money in an unprofitable business because hundreds of thousands have already been put into it. They may preserve a relationship solely because “we have been together for so many years.”
The problem is that past investments begin to be perceived as a reason to continue, even though, rationally, they should no longer enter into the decision.
Why does this happen?
First, it is difficult for a person to acknowledge a loss. If they stop a project, leave a relationship, or abandon an idea, they may feel that all their previous efforts were in vain. So we continue investing, hoping at least to justify the previous costs.
Second, we have a tendency to strive for consistency. If a person has supported a particular decision for a long time, it is psychologically difficult to admit that it no longer works.
Third, we often confuse perseverance with rationality. We think that giving something up means surrendering. But sometimes the ability to stop is a much more reasonable decision than continuing at any cost.
A good way to avoid the sunk cost trap is to mentally remove the past from the equation.
You can ask yourself:
“If I found myself in this situation today and had not invested anything in it yet, would I choose it again?”
For example, if you saw this business for the first time today, would you invest in it? If you received an offer for this position today, would you accept it? If you met this person today, would you want to build a relationship with them?
Such a question helps separate past investments from the future decision.
It is important to understand that the sunk cost principle does not mean you should readily abandon everything at the first sign of difficulty. Sometimes continuing a project really does make sense. But the argument should not be “I have already invested too much,” but rather “the future benefit justifies the future costs.”
That is the essential distinction.
Past costs can no longer be changed. But future resources, including time, money, attention, and energy, are still ours to allocate.
Therefore, when making decisions, it is useful to look not at how much has already been lost, but at what will happen next.
Sometimes the most rational way to protect your investment is to stop investing even more.
