"We ran out of luck years ago, Cain! And we've been running on fumes for Throne knows how long!"
Ciaphas Cain's story is relayed through his personal memoirs, published by his former lover, the Inquisitor Amberly Vail. In his memoirs, Cain claims to be a very different person than what Imperial propaganda portrays him as, being a coward who only accidentally became a hero when his actions for self-preservation ended up aiding the Guard in victory. Despite this professed cowardice, there are signs that Cain truly is a capable leader, helped by the fact that, unlike many commisars, he cares quite deeply for the welfare of the troops under his command. He is practically a grand-master with a chainsword, training himself further whenever he gets the chance as well as a crack shot with a laspistol.
Ciaphas Cain was first mentioned when The Emperor was answering a letter from Amberly Vail, asking if the reason for Cain's abnormal luck was because he was being punished by the Emperor, or was a source of entertainment for the Chaos Gods. The Emperor praised Cain as having "enough common sense to survive whatever the Chaos Gods threw at him," faring better than most who served the Imperium.
Ciaphas Cain is seen being celebrated by numerous guardsmen over his latest success against the Orks, in which his convoluted actions while trying to flee for his life only ensured Imperial victory once again and saved his men. In public, Cain accepts the congratulations of his troops. In private, however, Cain mentally breaks down over his intense imposter syndrome, believing that his luck is sure to run out soon, that innocents are dying to maintain his "bed of lies" and that he must confess the truth before fate finally catches up with him. However, he is interrupted by his Valhallan subordinate, Jurgen, who tells him that he will be presented with the Star of Terra for his bravery and that a representative of Ultramar was waiting to meet him. Cain quickly adopts his confident public persona once again, and accepts the award, telling Jurgen to show the "commander" in. However, to Cain's horror, it was none other than Marneus Calgar, who somehow hid behind the office door and overheard all of Cain's private confessions. Before Cain can sputter a fearful explaination, Calgar instead embraces him as his "mood kindred," as both of them suffer from their overwhelmingly ludicrous success and are "pieces of shit" in their own eyes. They proceed to pathetically sob in each other's arms for an unknown period of time.
Cain maintains two different personas. First is his cool, confident, and calm one, where he puts on a brave face for his troops. This, however, is only a mask for his true pain: he is a completely closeted coward but no matter what he does to save his own skin it somehow only aids the Imperium in victory and saves human lives, winning the admiration of his troops. No matter how well the scenario plays out, he feels undeserving and self-deprecates heavily, seeing himself as a "piece of shit". The cycle of close-calls with death and seemingly impossible victories take a heavy toll on his psyche.
Despite his cowardice and self-loathing, however, he is shown to care (at least somewhat) for the lives of his troops and inwardly hates having to lie to them. In the end, however, his cowardice will always put said troops at risk, even if it all works out in the end, so his own life is at the forefront. He does still want the cycle to end, desiring to confess and admit to being a fraud.