A. Midway through Harry Potter and the Philosopher's Stone, Rowling drops the reader a hint. "Erised stra ehru oyt ube cafru oyt on wohsi." Which is another way of saying "don't get too fixated on what happens here—it isn't real".
B. Purity of heart is to will one thing.
C. Megamind, with voice acting by Will Ferrel and Tina Fey, deserved more success than it got. A clever spin on the comic book hero trope, with a plot based in solid moral principles. You should see it. (4)
D. Rowling undoes her good hint at the end of Book VII, when Dumbledore tacitly endorses idealism during Harry's dream sequence.