Entrepreneurs often get burned by a failed investment (like a bad ad agency) and become hesitant to invest in that area again. This is a cognitive trap. The first loss was the money spent; the second, more significant loss is the opportunity cost of not trying again with a better strategy.

The effort invested in sourcing and negotiating a deal can create a psychological bias to complete it. To combat this sunk cost fallacy, ask: "If this opportunity appeared today with zero prior effort, would I still write the check?" This separates effort from the actual investment decision.

Individuals in debt often rationalize further spending with the logic, "I'm already in debt, what's a little more?" This sunk cost fallacy, combined with the desire for dopamine hits to alleviate financial stress, creates a self-reinforcing spiral of worsening debt.

A study by Barry Staw found that instructing decision-makers to "think about it as a new decision" has no effect on mitigating sunk cost fallacies. It's a mental trick that we fool ourselves into thinking works, but the data shows it's ineffective for making a more rational choice.

Gaonkar admits a major mistake wasn't just selling NVIDIA too early, but failing to re-evaluate it later. The sunk cost bias makes it psychologically difficult to revisit past decisions, especially ones that were wrong, causing investors to miss out on significant future gains.

The common advice to overcome sunk cost fallacy—"imagine you didn't own this, would you buy it today?"—is ineffective because you cannot truly ignore the reality of ownership. A more robust method is setting pre-commitment contracts or "kill criteria" that force a decision when specific signals are observed.

In auctions with uncertain value (like oil leases or even NFL draft picks), the winner is not a random bidder but the one with the most optimistic valuation. This often means the winner has significantly overestimated the item's true worth and is therefore 'cursed' by their victory.

Once people invest significant time, money, and social identity into a group or ideology, it becomes psychologically costly to admit it's wrong. This 'sunk cost' fallacy creates cognitive dissonance, causing people to double down on their beliefs rather than face the pain of a misguided investment.

To evaluate a commitment—be it a job, investment, or relationship—ask: "Knowing everything I know now, would I choose this again today?" If the answer is no, your attachment is likely based on past investment (sunk cost) rather than future potential, signaling it's time to reassess.