None of us enjoys the thought that what we do depends on processes we do not know; we prefer to attribute our choices to volition, will, or self-control.... Perhaps it would be more honest to say, "My decision was determined by internal forces I do not understand."As an example, I will offer some trends in my behavior that I cannot fully explain: Why my blogging tends to come in chunks, Why it takes me so long to take a shower when I come back from the gym, Why I still have not synced my iPod with my computer so that I can listen to podcasts, Why I decided to major in neuroscience, etc.
In general I find that I have more trouble to explain big life decisions than smaller ones, which is too bad because generally all anyone else cares about is my reasons for the big ones. If you would like to know why I wear Asics running shoes, I could come up with some solid answers. But nobody has ever asked me that!