Upon termination of a given policy, the amount of premium collected minus the amount paid out in claims is the insurer's underwriting profit on that policy. Underwriting performance is measured by something called the "combined ratio", which is the ratio of expenses/losses to premiums. A combined ratio of less than 100% indicates an underwriting profit, while anything over 100 indicates an underwriting loss. A company with a combined ratio over 100% may nevertheless remain profitable due to investment earnings.
Large loss: The size of the loss must be meaningful from the perspective of the insured. Insurance premiums need to cover both the expected cost of losses, plus the cost of issuing and administering the policy, adjusting losses, and supplying the capital needed to reasonably assure that the insurer will be able to pay claims. For small losses, these latter costs may be several times the size of the expected cost of losses. There is hardly any point in paying such costs unless the protection offered has real value to a buyer.
Collision coverage has a deductible, which is the amount you pay before your coverage helps pay for your claim. You can typically choose the amount of your deductible when you buy coverage. So, if you choose a $1,000 deductible and your car is later damaged in a covered accident, you'd have to pay $1,000 toward repair costs. Your collision coverage would help pay the rest, up to your coverage limit.