Psychology

A sunk cost is a cost that has already occurred and cannot be changed by the present decision.

Imagine spending €2,000 developing a product. That €2,000 is gone whether you continue or stop.

A forward-looking decision should therefore focus on information such as:

• —future costs
• —future benefits
• —future probabilities
• —available alternatives

But psychologically, knowing this is easier than feeling it.

Important distinction

Not everything connected to the past is a sunk cost.

• —Information learned from experience may still predict the future.
• —A mortgage may create future financial obligations.
• —Children create continuing responsibilities.
• —Leaving a job may involve future switching costs.

Those things can remain relevant.

Classic sunk-cost research found that prior investments of money, effort or time can increase people's tendency to continue an endeavour.

Later meta-analytic research found overall evidence for the sunk-cost effect while also showing substantial variation depending on the type of decision and context.

Therefore

• —The phenomenon has empirical support.
• —But it is not a fixed-strength rule operating identically everywhere.

Stopping can produce an emotional reaction.

The investment may suddenly feel:

• —wasted
• —lost
• —embarrassing
• —painful

Research has investigated whether negative affective reactions generated by sunk-cost situations contribute to sunk-cost responding.

Evidence suggests affect may be one part of the process.

Imagine a project going badly.

You already invested heavily. You receive negative feedback. Now you must decide whether to invest again.

This broader pattern is often studied as escalation of commitment. It overlaps with sunk-cost reasoning but is not identical to it.

Escalation research examines multiple factors that may sustain commitment.

Sunk cost effect ≠ escalation of commitment

Past investment can contribute to persistence. It need not be the only reason.

Sunk costs need not be purely monetary. Time and effort can matter too.

But different forms of investment do not necessarily produce identical effects.

In personal decisions people rarely think:

I've invested €12,600 into this relationship.

They may think:

• —“I've given this seven years.”
• —“I've worked too hard to become this.”
• —“I've sacrificed too much for this to fail.”

The psychological meaning of an investment may depend partly on what was invested and what that investment represents.

Research has directly examined sunk-cost effects in committed relationship decisions.

Experimental work using hypothetical unhappy-relationship scenarios found evidence that previous investment can influence willingness to continue a relationship.

However, results differed depending on the type of investment and experimental design.

This supports using relationship decisions as one possible application of sunk-cost reasoning. It does not support the claim: “People stay in unhappy relationships because of sunk cost.”

Relationship decisions can involve many additional factors:

• —love
• —attachment
• —children
• —economics
• —safety
• —hope
• —values
• —commitment
• —social pressure
• —and evidence about whether change is actually occurring

Sunk cost is one possible influence. Not a universal explanation.

Suppose someone says: “We've been together seven years.”

Those seven years may matter emotionally.

But if the only argument for another year is: “Because otherwise the first seven were wasted,” then the reasoning deserves examination.

Removing that argument still doesn't answer:

• —stay or leave
• —continue or stop
• —finish or pivot

It simply creates space for another question:

What does the evidence support from this point forward?