Young Goodman Brown reacts very coldly toward his wife and the people in his town after he's returned from his strange trip into the woods.
Why does he react strangely? He believes that he's seen pretty much everyone he knows -- including the most virtuous old woman of his town, the one who taught him his catechism -- on their way to or participating in the satanic mass in the forest.
Is he justified in acting this way? If what Young Goodman Brown saw was the truth -- that is to say, if he indeed witnessed all of his neighbors engaged in devil worship -- then maybe yes, he would be justified in maintaining cool relations with them. The narrator, however, adds more than a few terms -- such as "seems like" and "as if" -- in order to suggest very strongly that what Young Goodman Brown thinks he witnessed did not actually happen.