I used to think that information was destroyed in black holes. But the AdS/CFT correspondence led me to change my mind. This was my biggest blunder, or at least my biggest blunder in science.

"Stephen Hawking at 70: Exclusive interview" in New Scientist, (4 January 2012). In his comment that he "used to think that information was destroyed in black holes", he is referring to the black hole information paradox.