[quote]So fades the harvest of my betrayal[/quote] He was betrayed by the Librarian because he wanted to compose the entire human race to fight the Flood, she betrayed him and placed him in the Cryptum on Requiem. [quote]Even these beasts recognize what you were oblivious to human[/quote] Didact thinks that the Forerunners are the worthy inheritor of the Precursors mantle, not humanity, thus making them the species that must rule the galaxy. [quote] The Librarian left little to chance didn't she? Turning my own guardians, my own world, against me[/quote] Requiem was essentially the main shield world from which the Didact waged war with the Flood. It was his option to fight the Flood instead of the Halo Array. His Prometheans were turned by the Librarian in order to protect the place from anyone trying to access the Didact. [quote]But what hubris to believe she could protect her pets from me forever[/quote] The Librarian took special interest in humanity and devised plans to guide us after being de-evolved after the Ancient Human - Forerunner War. It's most likely that it's because we managed to defeat the Flood, and the it is said the Flood is challenge set by the Precursors to see if that race is worthy of the mantle. Humanity defeated the Flood, the Forerunners did not. [quote] If you haven't mastered these primitives, then man has not obtained the mantle. Your ascendance may yet be prevented[/quote] The mantle is a mythical right from the Precursors over who should be the galaxy's guardian and protector. Basically be the higher race that should guide all others to advancement and such. The Didact takes this as a reason to be superior and dominate the rest, even if the mantle is not corresponded to the Forerunners. [quote]Time was your ally, but now it has abandoned you. The Foreunners have returned. This tomb, is now yours[/quote] The time humanity had was given thanks to the Librarians betrayal of the Didact. Now that he is out again, he is out to compose the human race in order to fight the Flood, which is bound to be returning to the galaxy from dark space, as it did with ancient humanity. Take note that the Flood outbreaks we know have come from Forerunner installations in quarantine. Flood coming from outside the galaxy is thousands of times more dangerous and in even bigger numbers. Hope that helps. It's all in the novels. Particularly the Foreunner trilogy.