At its core, insurance is a mechanism for transferring financial risk from an individual or entity to a larger group. Members of this group share the losses of the few through pooled resources and calculated premium contributions, transforming uncertain individual exposures into predictable collective costs. The engine that makes this possible is the Law of Large Numbers: as the number of independent exposure units in a risk pool grows, actual loss experience converges toward the expected loss. This statistical principle allows insurers to predict aggregate outcomes with increasing accuracy, which is why a larger pool produces lower variance per policyholder and more stable underwriting results than a small one.
Insurance is not designed for every kind of risk. It covers pure risk, which involves only the possibility of loss or no change, while it does not typically cover speculative risk, where both gain and loss are possible. For a risk to be insurable, several conditions must hold: there must be a large number of similar exposure units, losses must be accidental and random, determinable and measurable, not catastrophic for the insurer, with a calculable probability of loss, and supported by an insurable interest. The principle of indemnity then requires that the insured be restored to approximately the same financial position as before the loss, neither better nor worse off. Insurance is also intended only for fortuitous events, meaning losses that are unexpected and outside the insured's control.
Together, these conditions define the boundaries of what insurance can and cannot do. When they are met, premiums can be reliably set and risk pooling becomes viable. Capital, in the form of surplus, provides a financial buffer to absorb losses that exceed expected levels, ensuring solvency. Regulators set minimum capital requirements based on the size and risk profile of the pool, making capital adequacy essential to insurer stability.