Consider the following scenario. You are learning a difficult argument for the first time, but your prior beliefs disagree with the conclusion of the argument. It takes you significant effort to parse the argument. But once you finally understand the argument, must you necessarily believe the conclusion until you can refute it with your prior knowledge? Does a complete understanding of the argument, which you have not yet refuted, constitute belief? It seems that it should not be so, but how, if you have followed the reasoning of the argument, understood it, and not refuted it?
Edit: Suppose that you've understood the argument in question. You cannot find any flaw with it, and your logical evaluation fully supports it. However, your emotional evaluation still rejects the argument, for some reason. Perhaps it strongly conflicts with your values. Does this conflicted understanding/evaluation of the argument constitute belief? Wouldn't it be irrational not to believe? If you do not believe, how do you resolve this conflict?