Hamlet's story about what happened to him at sea seems indispensable to our appreciation of his character. Heretofore we have liked and sympathized with the melancholy prince but have tended to regard him as pessimistic, negative, bookish, and very indecisive. His accidental murder of an old man hiding behind a tapestry does little to change our opinion of him. Then when he tells Horatio about his adventures on his aborted trip to England, we see that Hamlet is capable to decisive and courageous action. He displays sterling qualities under extreme pressure. First, he forges a substitute letter for Rosencrantz and Guildenstern to carry to England, thereby saving his own life. Then when the pirate ship attacks he unhesitatingly boards it by himself, without knowing whether any others will follow his example. This reckless daring is truly heroic. The ships separate and Hamlet becomes the pirates' sole prisoner--but they naturally prefer to try to collect ransom for such a distinguished captive rather than killing him. Like Julius Caesar before him, Hamlet handles the pirates with consummate skill.
Hamlet seems like a changed man when he returns to Denmark. He has not only proven his own courage and resourcefulness to the audience, but he has proven them to himself. He not only sounds like a different man, but he obviously feels like a different man. At one point he calls himself "Hamlet the Dane," meaning the rightful king of Denmark (Act 5, Scene 1). Claudius' treachery has backfired on him. He has signed his own death warrant by bringing out the slumbering regal warlike qualities in his melancholy nephew. Hamlet is now determined to kill Claudius, and we believe he will really do it rather than just continue to think about it. He knows he has to act quickly.
It must be shortly known to him from England
What is the issue of the business there.
It will be short. The interim is mine.
And a man's life no more than to say "one." (5.2)
Hamlet has become so regal in his bearing that we feel he will not only succeed in killing Claudius but will manage to convince everyone of Claudius' guilty usurpation and of his own worthiness to become King of Denmark. But Fate has other plans for him.