"My mum knew what would happen next. It would be Sirius or Lupin or even Petunia. And why should they suffer just to delay the inevitable? So they refused Dumbledore as Secret Keeper. They correctly guessed Riddle would target Pettigrew, the weakest of the Marauders. So they made him Secret Keeper, then began a considered campaign to marginalise him, belittle him, even. To make him think they were keeping him out of the inner circle and all the plans therein. It was psychological warfare against their friend, to drive him to Riddle. To save him being tortured by him. To play on his weaknesses and insecurities to ultimately keep him alive."