What do you mean by guessing the beginning without guessing the end?

For example, a very good friend of yours, whom I haven't seen for several years, suddenly called on you one day and chatted for a while. You heard from his conversation that he wanted to borrow money from you, which was the right start. You lent money to your good friend out of a relationship, and he also agreed on a time to pay it back. But when it was time to pay back the money, he just didn't come to pay back the money. I just can't guess the ending.