The Master's words stung. His last body had been alive for so long, fighting on Trenzalore, weary from age and the weight of guilt over the lives that were sacrificed in his name while battling his enemies, that it was a relief to finally regenerate. He welcomed the the thought of having another body, another personality, that he'd almost forgotten that in the body he had previous to that one, he cried and literally said he didn't want to go. There was nothing he could say to the Master, but lower his head and look at the floor, abashed.
"One moment at a time," the Doctor replied, speaking morosely from practical experience. "You take life one moment at a time." He swallowed hard then continued, "Then being in Atlantis is your chance to live in this body. Make sure you don't live to regret it."