In Chapter Eleven of her book Dynamic Characters, Nancy Kress warns against assuming your readers will share your assumptions about character. Even when the assumptions are shared-as in Kress's example of the mother losing the child-as a writer, you should not miss an opportunity to expand and increase the tension of the story. Sometimes detailing the torment the character is going through, the obstacles she faces in trying to solve the problem, is a way to strengthen the reader-character bond. Other times, as Kress notes, the details may slow the story down. You have to assess the needs of your story. It's a good idea to write out the scene fully the first time around, then cut later if you feel the need to speed things up.
Antinomy (the apparent contradiction of two elements) plays a part here. If your character's reactions CONTRADICT what the reader expects, that can create interest and tension. The reader will look at this contradiction as a type of mystery, and mystery compels reading on for an answer. So explore opportunities to characterize through contradiction. Keep in mind, though, that antimony is only apparent contradiction. Once all is said and done-that is, once your story is told-your reader must understand why your characters acted the way they did, and those actions must be logically motivated by the characters' attitudes and backgrounds. This is why this background work is so important. As you create your characters, spend time analyzing various attitudes they can have, both understandable and strange. Make a list of possibilities, and then choose the most interesting (but be prepared to provide sufficient reason for any unexpected ones).