"Then that answers your question," he said, his tone brightening slightly because they'd entered territory where he was much more sure of himself. "If you meet him and he asks you, you walk away. I did it. Martha did it. It hurts and it's hard..." his voice trailed off. "It's so hard," he breathed, "but you feel better afterwards." He looked at Rose. "I wouldn't trade traveling with the Doctor for anything," he confessed, "but I think the trick to it is knowing when to stop. Sometimes you don't get a choice, but when you do... you have to walk away with what he taught you and just be a better person than you were when he found you. Know what I mean?"