WHY DOES HAMLET DELAY?
The reason is: he's melancholic. This state of mind is quite unnatural to him and induced by special circumstances. The Schlegel-Coleridge theory states that Hamlet's ability to act has been eaten up by thought. Bradley states that Hamlet's reflectiveness played a certain part in the production of the melancholy and was only a contributory cause of his irresolution to act. Of course, melancholy once established only induced more and more thinking so it is a symptom as well.
HAMLET WAS NOT NORMALLY INDISPOSED TO ACTION
Nobody who knew him considered him a mere scholar who has never executed a deed. In the court he was highly considered although he was deprived of the throne by his uncle. He was the favorite of the people who have no inclination to love frail philosophers. He was fond of fencing and practiced even in his darkest hours. He must have usually been resolute and fearless: how else would he have followed the ghost, how would he have killed Polonius, dealt with the king's commission, boarded the pirate ship, leapt into the grave, executed his final vengeance?
WHAT DOES HAMLET'S MELANCHOLY IMPLY?
He was inclined to nervous instability, to mood-swings.
He was easily consumed and for a long time by moods whether joyous or depressed. This meant "melancholy" to the Elizabethans, and indeed, the theory of temperaments was so familiar in Shakespeare's time that he may have made Hamlet melancholy on purpose. He gave to Hamlet a temperament which would not develop melancholy unless under certain exceptional circumstances.
HAMLET IS A DISILLUSIONED IDEALIST
There is in Hamlet an unusually sensitivity to moral good and evil - in the broadest sense of the word "moral". He had the soul of the youthful poet, an unbounded delight and faith in everything...