A more thorough explanation:

A basic mistake is an error, misconception, or misunderstanding that forms the basis of a transaction. It can be a mistake of fact or law and can be made by one or both parties to a contract. If the mistake is serious enough, it can render the contract voidable.

• Party A sells a car to Party B, believing it to be in good working condition. However, the car has a major mechanical issue that Party A was unaware of. This is a mistake of fact and could be grounds for Party B to void the contract.
• Party A and Party B enter into a contract, but Party A misunderstands the legal implications of a key term. This is a mistake of law and could be grounds for Party A to void the contract.

These examples illustrate how a basic mistake can affect the validity of a contract. If one party is operating under a mistaken belief, it can undermine the mutual understanding necessary for a contract to be enforceable.