That's a bit of an exaggeration. Mascara in the eye happens very often, to me anyway. What's really painful is the hairs off the mascara brush detaching and insinuating themselves under the eylid. That. hurts.
> Mascara on your retina would most likely end up in a hospital visit.
... And likely blindness. The retina is the inside of the back of your eye, where the optic nerve attaches. If you have mascara on your retina, it means you have punctured your eye.
Having something between your cornea and eye lid, while extremely irritating and painful - especially if a scratch results, is far, far less painful than having something puncture your cornea. Trust me, I've had surgery behind the cornea and had the anesthesia wear off.