BrotherOfBone wrote:
Astartes do feel fear and they do feel hopelessness.
The Brotherhood of Despair (I think they were called, tey're in the CSM codex). Basically they were being sent on all the most dangerous missions, losing loads of battle brothers, taking serious casualties and they became hopeless, they thought that the next mission would end in a placement somewhere different but they kept being sent on suicide missions.
They became so wracked with grief that they turned to Chaos.
IIRC, don't quote me on this one but that's about right.

 Toastedandy wrote:
I actually really like it. Seems similar to the Iron warriors in that the marines feel used and unappreciated, that they're merely a means to hold back a never ending tide when they have the potential to be so much more. Seeing his comrades die in droves (If your fighting Iron warriors, casualties on both sides will presumably be high), and fighting in continuous meatgrinders, your only hope is the light of the emperor, which you see less of each day, would understandably make you question your beliefs. And instead of letting your wavering faith spread to your brothers, your put down in some thinly veiled warning posing as a religious ceremony.

Mantra is very similar to the Iron warriors, except not as cheesy.

 Unyielding Hunger wrote:

 BrotherOfBone wrote:
Astartes do feel fear and they do feel hopelessness.
The Brotherhood of Despair (I think they were called, tey're in the CSM codex). Basically they were being sent on all the most dangerous missions, losing loads of battle brothers, taking serious casualties and they became hopeless, they thought that the next mission would end in a placement somewhere different but they kept being sent on suicide missions.
They became so wracked with grief that they turned to Chaos.
IIRC, don't quote me on this one but that's about right.

Just found them, but they're actually called the Company of Misery, formerly the Desolate Brotherhood.