Thread: What does it mean when people say that you "can't make up for lost sleep"?

I sometimes see people claim this on various sites that are in some way focused on sleep, and I think it sounds kind of weird.
If you can't make up for lost sleep, then why do you feel completely rested after sleeping a couple hours longer than normal for a couple days?
When someone says that you can't compensate for lost sleep it kind of sounds like you can never feel rested again once you have stayed awake all night once, or something like that.

Do they mean that loss of sleep causes permanent damage to the brain in a way that doesn't directly affect how rested we can feel?
Or what's going on here?