Accidents are real
Accidents occur. And accidents are unexpected. Nobody goes out in the morning saying: "You know what? Today I'm going to have an accident." That's why we call them accidents and not planned events: nobody knows there is going to be one until it hits. Car accidents, fires, hurricanes, major health problems, disability, etc.
Insurance is a bet
If you don't want (or can't afford) to pay the entire monetary costs associated with an accident, then you must get insurance ahead of time. An insurance policy is a legal contract between you and the insurer. When you buy insurance you are placing a bet on an accidental event. Obviously you hope it will never occur, but if it does, you get paid.
You pay a certain amount of money ("premium") to place a bet with the insurer on a certain accidental event ("coverage") defined in the contract ("policy"). If the covered accidental event occurs to you, with all the monetary costs that follow, you will first pay some money ("deductible") out of your own pocket, and then file a claim with the insurer to have him pay the rest (up to the agreed limit).