One psychologist that I know said it is human nature to think and mentally prepare for the worst. People don't want to be 100% certain of a positive outcome then be dealt a negative, fearing that would feel worse than being primed for letdown.
The inner voice is constantly creating roadblocks for us. It talks us out of picking up the phone to make a sales call. It explains all of the potential disasters related to speaking in public. It analyzes every situation and puts its own spin on things, changing our perception of events and people.
Can anyone relate to that? I sure can.