Before he was Corypheus, he was Sethius of House Amladaris. This magister of Tevinter was reportedly an obsessive believer in Dumat - a fact safe to assume given the passion with which the ancient Tevinters dedicated themselves to their Old Gods.
Sethius of House Almadaris was middling and wanted more. And like many who are weak at heart, he likely did not consider that it was his own nature that determined his place. He believed the whispers of demons, and he and six others breached the heavens to worship their false gods in person. Instead they found the rebuke of the truth. And in his punishment, Sethius became corrupted, became Corypheus. Instead of humbling him, this inflated his stature and sense of perceived destiny.
We are told that after his original fall in -395 Ancient there was a dormancy of some kind. Perhaps it was not unlike the slumber of the Old Gods. When he awoke again in -191 Ancient, it is clear Corypheus was understood and dangerous. The Grey Wardens caged him instead of risking a failed attempt at killing him - and well they did, for in the mishap with the Champion and in the preliminary battles with the Inquisitor. Corypheus maintained a tenacious hold on life.
The lesson Corypheus learned from his first attempt at breaching the Fade was not that it was wrong to dare, but that he had not dared enough. This despite the cost paid by all the world and, given his scarring, what Corypheus had personally suffered. But he did not, because the Inquisitor, above all else, broke this “Elder One” of his own delusions. What we witnessed when Corypheus disappeared was not the swagger of a conqueror, but the stumbling of a broken authority. In his first ascent, Corypheus was cast down by the Maker, perhaps, in his own mind, making him worthy of such. In this second attempt, it was a mortal, the Inquisitor.