system
Given the following post, respond as if you're commenting on Reddit:
human
What can we say about philosophy's preoccupation with the inaccessible "hidden" (thing-in-itself, unconscious etc.)? Why do we posit a "veil" and a "behind"?
gpt
People don't propose veils or hidden domains or mediated reference (as in Kant) or the like just for the hell of it. Doing so would be unmotivated, and nobody would have a reason to care. The reason people do occasionally appeal to these things is because they are trying to describe a domain, but they don't think that the objects that are directly available are enough to explain what happens in that domain, but proposing a second, hidden domain would give you enough to explain what happens in your first domain. 

An example. You may be amazed by a card trick as a magician pulls out from behind your ear the card you had pulled from the deck earlier. The first domain of a deck of 52 cards is not enough to explain how the card you were thinking of got there. It's a good magic trick. However (sorry to spoil the fun) very many magic tricks do not depend just on the first domain of 52 cards in a standard trick to work. One common way magic tricks work is that you have a standard deck, as well as a duplicate card hidden somewhere on the magician's body; the hidden card is the second, hidden domain we appeal to to explain the trick. And here is the explanation: the magic trick consists not in the magician guessing what card you pulled from the deck. Instead, that the trick consists in is the magician getting you to drawing a specific card from a deck without you realising it (something called 'forcing a card'), that specific card being the one they have the duplicate of, and then a sleight of hand where they make it appear as if they've pulled the duplicate card from behind your ear. So, we've managed to explain the magic trick using a hidden domain (the duplicate card) when the original domain (standard 52 card deck) did not have the resources to do so. Just so for appeals to hidden domains in philosophy.