Cobra Effect

How it works

Well-intentioned interventions often produce the opposite of their intended effect when people respond strategically to new incentives.

This model helps you recognise situations where this pattern is at play and adjust your thinking accordingly. Understanding it does not make you immune, but it gives you a framework for catching it in action and making better decisions as a result.

Case study: How Hanoi’s rat bounty created a rat-breeding industry

In colonial Hanoi in 1902, the French colonial government was struggling with a rat infestation in the city’s modern sewer system. Their solution: pay citizens a bounty for each rat tail brought to the authorities. The logic seemed sound — incentivise rat killing, reduce the rat population.

Instead, officials began noticing rats in the streets with no tails. Citizens were catching rats, cutting off their tails for the bounty, and releasing the rats alive so they could breed and produce more tails. Worse, enterprising residents began breeding rats outside the city to harvest their tails. The rat population increased.

The cobra effect — named after a similar failed bounty scheme involving cobras in Delhi — demonstrates that when you create incentives to solve a problem, people may find ways to benefit from the incentive that worsen the underlying problem. The solution became the cause.

When to use it

Apply this model whenever you notice its pattern appearing in your decision-making, your team’s behaviour, or the systems around you. It is especially valuable in high-stakes situations where the cost of this error is significant.

Try it now

Think of a recent decision or situation where this model might have been relevant. How would your approach have changed if you had explicitly considered it?