What do you think Goodman Brown has been forced to accept?

I think Brown has been forced to accept the dual nature of humans.  Prior to his little venture into the woods with Satan himself, Brown believes, as a devout Puritan, he is predestined for heaven.  He states that once he returns to faith he will cling to her skirts and follow her to heaven.  However, as soon as he enters the woods he begins to see that the people around him, who Brown thinks are virtuous, may not be so great.  For example, he learns that the devil knew his father and grandfather.  He also learns that three of the people he respects most, Goody Cloyse, Deacon Gookin, and the minister are also well acquainted with the devil.  He never is able to reconcile this and that is why he dies a bitter man.

It is interesting to note that Brown never accepts the duality of sin in himself.  He is able to see the sinful nature in others, but does he see it in himself?  Just look how easily he gets lured deeper into the forest, despite his declarations to turn back.  Eventually, he is even driven to rage and tear through the woods so that he is the most frightening thing in it.  Maybe if Brown had been able to recognize his own sins, he might have been able to accept the sins of others and lived a happier life.