I once watched "The Omen (I am now referring to the remake version that was the one that spooked me)," and when I watch Damien Thorn do all that nasty stuff, I have an urge to stop him, even though I know fate (or rather, the scriptwriters) had him go through the process of successfully completing his mission and grow up to be an Anti-Christ. And if you know me well, I would always follow me heart than my mind.
I guess you could call it faith. I watched a few anime, and they talk about this several times, about how the hero/heroine would go through all that pressure and obstacles of 'fate' to achieve his/her goal, wanting to fight against the heavens, and they claim it was because of the undenying human spirit.
Well, I don't completely disagree with that. I would fight, too, to survive. Call me selfish and everything, but that's just how I am. I will fight till the very bitter end to survive, because if there's one thing I hate more than living, is death. In fact, I fear it. So, the fear would drive me enough that I would pull all the stops to stop that baby from growing up into a man, even if I have execute him myself.
Of course, it would take an enormous amount of boldness from me (not courage). Killing an adult man is scary enough for me, let alone killing an infant.