Dan Abnett said this quote
“ Enemy?’ Horus laughed. ‘When did they become the enemy? They are men like us.’ He glared up at the night sky, threw back his head and screamed a curse at the stars. Then his voice fell to a whisper. Loken was close enough to hear his words.‘Why have you tasked me with this, father? Why have you forsaken me? Why? It is too hard. It is too much. Why did you leave me to do this on my own? ”