Good question. It's probably a combination of inertia, taking the path of least resistance, and choosing not to give up. I'm also an optimist so even if I go through periods when I' full of doubts, I eventually find a reason to be optimistic again. Not sure if that answers your question.
Here's an idea. Ask me anything, and I'll try my best to give you a real answer. My answer will probably be longer than your question, which means you make XEC in the exchange =)
What keeps you going when you don't know where you are headed?