Sentence:  As long as the most difficult <WSD>instance</WSD> you've tried is Gnomeregan, you're never going to be credible talking about 'difficult encounters'. 
Meaning of the word marked with <WSD> tags:  A dungeon or other area that is duplicated for each player, or each party of players, that enters it, so that each player or party has a private copy of the area, isolated from other players.