Deck FAQ: Discard vs Remove
Discard: a used card goes to your Discard Pile; it is shuffled into a new deck only when your deck is empty and you must draw.
Remove: the card leaves the game and returns to the box.
Removing cards (Trading Post, Faerie Ring, Witch Hut, Library of Enlightenment) thins your deck.
A used card goes to your personal Discard Pile and will return when you reshuffle (your discard is shuffled into a new deck only when your deck is empty and you must draw). A REMOVED card leaves the game completely and returns to the box - removing cards (Trading Post, Faerie Ring, Witch Hut, Library of Enlightenment) is how you thin your deck so the strong cards come around more often.