My wife refused to get a helmet when we got bikes because "I've never had an accident on a bicycle and we don't go fast enough to need it" , so I said "Fine, we'll have this discussion after the first ride"

I got up to the top speed of the speed-controller ebike, she followed, and when we stopped it old her to imagine a puppy runs out in front of her, she has nowhere to go but straight into a wall and smash her head into the concrete, the trees and smash her head into the wood, or jump off the bike and smash her head into the pavement. Because in a crash, your head is going to hit something, and in this case you could be the most careful person on the planet but you can't stop a puppy, or child, or DUMP TRUCK from blocking your path and forcing you to make a hard choice in less time than it takes to sneeze.

She decided to pick a helmet.

The hard surface your head will bounce off or grind into will not be nice about you failing to wear a helmet. Neither will I.