I subscribe to the school of thought that believes every smll detail makes a different, it is called the butterfly effect. Killing a butterfly can cause a tidal wave half way around the world.* The other schoool of thought is that, short of accidentally inventing a zombie virus, no single choice can cause a huge life change.
I believe the butterfly effect to be true because I have experienced it. I can't think of an example now... but it is true; everything in my life is a result of a tiny thing. Literally, I am sure I dropped a drink once and that if it weren't for that I would not be gay-- well, maybe that is a stretch.
*There are several different versions of the butterfly effect, all contain a butterfly and a tidal wave.