The very real possibility that you will fail. This is not an if/then world. Substantive points of reference are very fleeting; so much so that when one comes along, seeing it and convincing yourself that you are seeing what you think you are seeing is more difficult than you might think. Learn to marshal the courage to walk away from something that you've invested so many hopes in. Sorry to sound so negative about things but there are more than a few people that have hung themselves with this particular rope.
I agree, and I think you sound realistic on this. The human brain is prone to believing in things it sees or thinks about a lot, and it is true for most areas of our lives that it is hard to give up something you have invested hope and effort in.