Most of us, myself included, had no idea.
I’ve had 1 ride in a F-16 D model and went thru a whole 45 mins of training on them. They have small rocket under the seat that pushes you out at roughly 10G.
If you don’t have your body in the right position it can break your legs or other bones. Thats not saying anything for whats forcing you to eject in the first place. Once you do eject you get hit by the wind stream which can also cause injury.
As explained to me its an extremely violent experience. But it beats the sudden stop and burning to death thing.