it cannot be unseen.
I never understood this expression. Why would you need to unsee something?
it means to forget something.
It means you saw something really terrible, so much so that you can't get it out of your head and you wish you'd never seen it.
I don't get it.
Step 1: You saw something utterly disgustingStep 2: You wish you hadn't
Step 1 is where the confusion is.
Disgust is an emotion that is typically associated with things that are regarded as unclean, inedible, infectious, or otherwise offensive.