"Right and wrong aren't paired up with sometimes right and sometimes wrong, Jack. Either it's right, or it isn't. You should make your calls based on what's right."

He focused his train of thought and, after announcing he'd just done that, began to speak about the Master.

"Oh, we used to play tricks on each other," the Doctor said. "Used to practice psychic interference wave augmentors in order to disrupt each others' projects. Once---" and this made the Doctor terribly excited, "--I rigged up a complicated psychic interference program within his project. He'd spent the better part of a decade on this project and the program went off not before he turned it in, not right after, but while he was doing the experiment for the class council. And it didn't just not work, the whole thing fell apart, like a house of cards that had the bottom pulled out. Oh, it was glorious."