Continuing because of what you have already put in is the sunk cost fallacy. That money is gone whichever option you take, so the comparison should only be about gains from here. Sitting through a film you dislike and holding a losing investment share the same structure. Asking 'if I were deciding fresh today, would I choose this?' usually settles it. What makes sunk costs dangerous is that the more you have put in, the harder it is to stop, so you keep pouring in more in the direction of a bigger loss. Setting a stopping rule when you begin makes the trap much easier to escape.
You see what you want to see
Once you settle on a conclusion, information supporting it becomes unusually visible, while contrary evidence gets picked apart. The practical defence is searching for the counter-case yourself first. Writing down in advance what you would expect to see if you were wrong makes it firmer still. Asking someone you trust to deliberately point out the weaknesses in your conclusion also works. If you only consult people who already think like you, you are collecting agreement, not checking.
What comes to mind easily seems common
When judging how often something happens, people lean on how easily examples come to mind rather than on actual statistics. Accidents that get heavy news coverage feel more common than they are, while quiet risks are underestimated. Hearing mostly about people who succeeded makes a path look easy for the same reason: those who failed rarely tell their story, so they simply go unseen. When a judgement seems to rest on a vivid impression, looking up how many cases there are out of the whole is the surest correction.
Doing nothing is also a choice
Not changing feels safe, but keeping things as they are is itself a decision with its own cost. Not cancelling an unused subscription, or leaving a product whose terms have worsened, both belong here. Asking whether you would sign up today if you were not already using it makes the call easier.
Sunk cost: leave what is spent out of the calculation
Confirmation bias: look for the counter-case first
Status quo: keeping things has a cost too
Anchoring: do not be pulled by the first number
The first number becomes the reference
In negotiation or shopping, the first figure presented becomes the reference point for everything after. It is why showing an original price makes a discount effective. Deciding what you consider reasonable before seeing any number reduces the pull. The unsettling part is that even an absurd first number has an effect. The larger the sum at stake, the more worthwhile it is to find two or three comparisons yourself.
Record why you decided
Memory rewrites itself once you know the outcome. Good decisions get remembered as good judgement, bad ones as unavoidable. Two or three lines written at the moment of deciding let you check later what you actually misread. Judgement grows from records, not from experience alone. The record need not be elaborate: the date, what you chose, why, and what result you expected are enough.
Judging decisions by their results
A good outcome does not mean the decision was good, and a bad outcome does not mean it was bad. Under uncertainty, sound reasoning can still meet bad luck, and a reckless choice can happen to pay off. Grading only by results leads you to repeat lucky recklessness and abandon unlucky good judgement. When reviewing a decision, look separately at what you based it on, given the information available at the time.
Checks before an important decision
Not every decision needs this treatment, but for one that is hard to reverse or involves a large sum, a few minutes with the questions below is worthwhile. Simply leaving it for a day and looking again filters out a good deal of impulsive judgement.
If I were deciding fresh today, would I choose this?
What would I expect to see if my conclusion were wrong?
Where did the reference number come from?
Have I written my reasons down in two or three lines?