Eh, eh, huh, what?
Hardest part with hearing is that damage is cumulative, so shooting a couple rounds suppressed without earpro each time at the range rarely leads to an immediate "Oh shit!" reaction and by the time it's something that can be actively noticed, there's no fixing it. Nothing like realising the cymbals or piano in a favorite song didn't just disappear, you just can't hear then any more.
Convincing people of that (and that auditory exclusion when adrenaline is going doesn't preclude severe hearing damage, you just don't notice it until later) is a bitch.