This post is long and probably boring and got spoilers and I'm really sorry, but it's necessary to illustrate...
There was a Russian game called Pathologic that came out a few years ago. I played a doctor who had come to a small town (circa 1910) and quickly became embroiled in a desperate battle against a cataclysmic infection spreading through the whole population. By the fifth day, the infection proved so elusive that the doctor had realised that the only way to obtain a sample of the infectious cells was to take them from the heart of a fresh corpse.
The good doctor had been told of the whereabouts of a Haruspicus, a shamanistic surgeon, an expert in cutting open the dead. Just the kind of man I needed. But somewhere along the way, a disturbing hunchbacked man had offered me a massive sum of money to find his missing daughter in the town. I soon found her in a tavern, dancing half-naked for money and to appease the menfolk, terrified of the growing disease outside. She told me that the hunchback had killed her real father because he loved her, and wanted her for his own. She did not wish to go back to him, she wanted to escape. She needed my help. I agreed to meet her again, in the Tanner district at 9pm, where we might talk more freely.
I left the girl, and later located the Haruspicus. As I had just broken him out of prison, he readily agreed to help me 'find' a fresh body. He would go to the Tanner district. At 9pm. I was to meet him there.
You all can make a fairly accurate guess at this point as to where this is going, but you have to understand that the girl was an optional side quest. I could have told the hunchback to get lost, to keep his money. I had no idea, no idea what would happen. I have to tell myself this. I did not make it to the Tanner district in time - I was exhausted and needed sleep. By the time I got there, the Haruspicus was nowhere to be found. But there, sprawled on the side of a nearby alleyway, I found the body of a half-naked woman. A girl. A daughter. Her.
I tore out her heart, and I threw the cells, drenched in the infection, beneath my microscope. I told myself it had been necessary. I told myself many things. Over the next few days, I killed many people. I saved many more people. But I did not save her.