In his debut episode, the Tenth Doctor declared to the Sycorax Leader that he was the type of man to give no second chances. In other words, if you didn't take his initial offer of peaceful retreat, he would destroy you. And then he was reunited with Lady Cassandra. Lady Cassandra was the self-proclaimed "last of the humans" and almost killed everyone aboard the space station in The End of the World before the Ninth Doctor was able to stop her and destroy her. When the Tenth Doctor met her, however, he didn't immediately invoke that "no second chances" clause he has so heroically proclaimed in the previous episode. In theory, he should have played that card immediately. No second chances... unless you're a trampoline.