An accident is something that happens even though nobody intended for it to happen. It’s also a euphemism for “crash” — instead of saying “car crash,” we say “car accident.”
It’s easy to see why we like “accident” better than “crash.” A crash is very serious and scary. People can be hurt or killed, and cars — which usually seem stable and safe and strong and completely under our control — can be mangled beyond recognition.
We use euphemisms to avoid unpleasant thoughts. Everyone knows that “car accident” means “car crash,” but we say “accident” because it sounds nicer — more like knocking over a glass of water at dinner than the sound of a windshield shattering against the pavement.
This is important: With euphemisms, you don’t have to imagine how the thing you’re avoiding looks or feels or sounds. Some euphemisms are invented precisely to prevent you from imagining those things.