When prospects meet you for the first time, they likely already have a positive, negative or neutral impression of you. The mindset they come to you with can help determine whether they eventually decide to do business with you.
Our preconceptions about others often play out in the way we think they will. It's really no mystery, just human nature and psychology. If people come to the table wanting to work with you, they will search for evidence to support their initial inclinations—even if you don't deliver the perfect presentation.
At the same time, if they come to the table not really wanting to work with you, they will be looking for reasons to be right and choose not to work with you. It's true in politics, in business, in dating and in life. We want to be "right," and often that need works against our own best interest.