Is Ophelia connected in any way with the crime Hamlet seeks to avenge? Why is he so brutal to Ophelia in Act III, Scene 1? Why does she go mad?
The answer submitted by rowens to your question is thorough, though my secret doubt is that Shakespeare was more concerned with theatrical effect than consistent motive.
Ophelia is not a strong character. She acquiesces to everyone; her brother, her father, and to Hamlet. But the inner workings of her mind are unexplained. The fact is that we don't know why Ophelia goes mad; we can only speculate. But madness was a common element in the revenge tragedy, and Shakespeare's audience would have expected somebody to go truly mad at some point. Just as a ghost would have been a necessary ingredient to the story.
Hamlet's rage at Ophelia is more easily explained. Many performance have staged the scene that Hamlet becomes incensed because he realizes that somebody is eavesdropping, and it's obvious that Ophelia knows. On the other hand, Hamlet's reaction seems a little extreme. Perhaps he's not as sane as he says!
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