Hamlet's hand is stymied for a couple of reasons, most of which are laudable. While the young prince beats himself up for not taking immediate action as the Ghost demands ("Conscience doth make cowards of us all" 3.1.82), Hamlet believes he must have definitive proof before carrying out the Ghost's commands, which are to kill the usurper (Claudius) and let his mother (Gertrude) stew in her sin:
If thou hast nature in thee, bear it not.Let not the royal bed of Denmark beA couch for luxury and damnèd incest.But howsoever thou pursuest this act,Taint not thy mind, nor let thy soul contriveAgainst thy mother aught. Leave her to heavenAnd to those thorns that in her bosom lodgeTo prick and sting her (1.5.81-88).
What if it tempt you toward the flood, my lord,
Or to the dreadful summit of the cliff
That beetles o'er his base into the sea,
And there assume some other horrible form,
Which might deprive your sovereignty of reason
And draw you into madness? think of it:
The very place puts toys of desperation,
Without more motive, into every brain
That looks so many fathoms to the sea
And hears it roar beneath (1.4.69-78).
Do not forget. This visitationIs but to whet thy almost blunted purpose (3.4.111-113).