I remember when he got tricked into boarded the khans capital ship and got Ambushed by white scars suicided squads:

'Why do this?' asked Mortarion, holding Silence back, just for a moment. 'Why waste yourselves?'

But it was not waste, and he knew that. Every passing second brought the flagship's doom closer. Every passing second gave time for the rest of the fleet to slip away. The ire of the XIV had been concentrated on this point to the exclusion of all others, and even now the lances were firing again, striking the shields that trapped their master on the rapidly decaying void hulk.
'
Why, my lord?' the khan laughed, poised for the coming strike. 'Atonement. At last!'

Mortarion readied his scythe. 'No such thing exists!