"You make a promise that has to be kept," Malfoy said. "That's all. At some time in the future, the person you made the promise to can call it in. It's like a life-debt."Harry is desperate enough to ask Malfoy for help who agrees if Harry will make a promise. In the end Harry asks for 5 favours and gives 5 promises to Draco. Draco is very Slytherin in this story, successful, intelligent, cunning and yet somehow tragic hero. He sort of gets what he wants but only watered down version of his wish. Harry biggest fault is that he didn't give Malfoy enough credit and that he was too much in love and happy with Ginny that he lost caution and steeped in the trap. Magic. Obsession. Addiction.