One thing they need

Karyn said "Okay, Jon, I want to try one more thing. Jon, from now on when I make a change you remember both before and after the change, unless I specifically say you don't." Jon replied, "How would you know something like... oh, yeah. That must be true now." "Jon, you have blonde hair." Suddenly, Jon did indeed have blonde hair, and he had a very confused look on his face. "That's... that's strange. I remember my hair is blonde, but I know it's changed and I remember the way it originally was too...." "That's good," said Karyn. "Your hair is its original color again. Now, how about a bigger change?" "A bigger change?" "Sure, Jon. You're my..."