Often, when faced with a monumental choice, we know right away what we want to do. The head/heart controversy, the positive/negative evaluation, the looking at it from all angles - these are all ways we undermine our true desire and judgement. Although we know right off what we want to do, we become scared of the imagined consquences and then become unsure. So we start to pick it apart and second guess ourselves in order to delay a decision and to give the appeance (to others AND ourselves) that we are thinking carefully and not acting impulsively.
I don't say you should not think about what you are going to do. But give a real lot of weight to that initial judgement. Listen to it very closely, and go against it at your peril. In my life - the quality of my decisions have had NOTHING to do with how much time I spent thinking about them. In fact, it's been the opposite. Most of the time, you know what you want to do right off the bat. Do THAT.
That is not the head, and it's not the heart either.
It's the gut.