An insurance policy is called a unilateral contract. The practical consequence is that:

解析

Only the insurer gives a legally enforceable promise, namely to pay covered losses; the insured merely pays premium and can stop at any time, which is why an insured cannot be sued for declining to renew. The equal-value description contradicts the aleatory nature of the contract. Note that the promise is still conditional, since the insurer owes nothing until the policy conditions are met.