Definition
Picture an unfair card game where only one player can see everyone's cards. Information asymmetry is what happens when you buy, sell, or sign a contract and one side has much more, or much more accurate, information than the other. The balance of knowledge is broken. This gap is a classic reason economic activity goes wrong. Good-quality goods can vanish from a market while flashy but poor ones stay. Or, after a contract is signed, someone can start acting differently behind the other side's back.
Suspicion Born in the Used-Car Lot
Picture a customer and a salesperson at a used-car lot. The salesperson knows whether this car was ever flooded and whether a serious engine problem is hiding inside. The customer sees only the shiny paint and the numbers on the dashboard. What's really under the hood is hard to know.
The customer worries about being fooled into overpaying. So they're only willing to pay a so-so, middle-of-the-road price for any car on the lot. Then the owners of truly well-kept cars, who deserve a higher price, leave the market so they won't lose money.
In the end, the market fills up with cars that look fine outside but are broken inside. When the side with less information ends up choosing the worst partners or goods because of its disadvantage, it's called adverse selection.
The Change of Heart After the Deal
Unequal information causes trouble even after a deal is done. Before buying phone-damage insurance, someone might put a case on their phone and handle it with care. Then, the moment they get insurance that covers full repair costs, they start treating the phone roughly. That's a classic example.
The insurance company can't follow customers around 24 hours a day to see how carefully they handle their phones. Taking advantage of the fact that the other side can't fully watch your behavior, and becoming less careful or less responsible, is called moral hazard.
The same goes for a company owner who hands the business to a professional manager. The manager may chase their own bonus and reputation instead of the shareholders' interests. This happens because the owner can't see the manager's hidden actions and intentions clearly.
To Be More Precise: Ways to Close the Gap
To be more precise, information asymmetry doesn't always wreck a market or stop trade. People have kept developing clever fixes so that they can overcome distrust and trade with peace of mind.
Sellers who want to show that their goods are truly good make strong promises, like a 100% money-back guarantee or three years of free checkups. These promises cost little for someone selling good goods, but they're nearly impossible to keep for someone selling junk. Proving your trustworthiness this way is called signaling.
Buyers and companies with less information don't just sit back and take it, either. An insurance company might cut premiums sharply for customers with no accidents. A buyer might carefully read real users' honest reviews and star ratings on a food-delivery app. Many such efforts to narrow the information gap together keep markets healthy.
Common misconceptions
Information asymmetry only happens when a seller lies or commits fraud.
Even without fraud, it exists whenever one side simply knows more than the other about a product's real flaws or about specialized knowledge.
Where you meet it
A renovation contractor knows the real cost and quality of the materials far better than the homeowner does.
A landlord knows about a building's noise between floors and seasonal leaks much better than a new tenant does.
In one sentence
It's when an information gap between the two sides of a deal leads to bad goods being picked or to irresponsible behavior.