The possibilities are endless. Humanity limits itself in such a way so that life isn't so huge and more manageable. For me, I do what I can deal with in my soul. I have the thought, "now, in ten years, how well is this going to sit with me?" In other words, I will not burden my soul with something that I don't think I can deal with in the far future.
As we grow older, we become limited by fear and a lack of resources- whether these are real resources or just the capacity to figure out a way to circumvent an obstacle is irrelevent. I understand the logic of this. But, as Spock in Star Trek learned, the logical decision is not always the best one to make. So what if there's only a 4% possibility of success? If it's the right thing to do, then that is what must be done.