Quote 7
HAMLET
The spirit that I have seen
May be the devil: and the devil hath power
To assume a pleasing shape; yea, and perhaps,
Out of my weakness and my melancholy,
As he is very potent with such spirits,
Abuses me to damn me. I'll have grounds
More relative than this. The play's the thing
Wherein I'll catch the conscience of the King.
(2.2.627-634)
Here, Hamlet is worried that the ghost might be lying about Old Hamlet's death in order to lead young Hamlet astray. Hamlet wants to be sure that Claudius is guilty so he devises a plan to test the ghost's story. Sounds pretty logical—i.e. not crazy—to us. We'd want confirmation of our spirit visitations, too.
Quote 8
HAMLET
Now might I do it pat, now he is praying,
And now I'll do 't. [He draws his sword.]
And so he goes to heaven,
And so am I revenged. That would be scanned:
A villain kills my father, and for that,
I, his sole son, do this same villain send
To heaven.
(3.3.77-83)
Once again, Hamlet finds a reason to not kill Claudius. His rationale? He says he doesn't want to murder him while the man is praying because he's afraid he'll send Claudius' soul straight to "heaven." Revenge, for Hamlet, isn't simply about killing Claudius —it's about making sure he suffers in Hell, just like he thinks his father is doing.
Quote 9
HAMLET
[…] I do not know
Why yet I live to say 'This thing's to do,'
Sith I have cause, and will and strength, and means
To do 't. Examples gross as earth exhort me:
Witness this army of such mass and charge,
Led by a delicate and tender prince,
Whose spirit with divine ambition puffed
Makes mouths at the invisible event,
Exposing what is mortal and unsure
To all that fortune, death and danger dare,
Even for an eggshell. Rightly to be great
Is not to stir without great argument,
But greatly to find quarrel in a straw
When honor's at the stake. How stand I, then,
That have a father killed, a mother stained,
Excitements of my reason and my blood,
And let all sleep, while, to my shame, I see
The imminent death of twenty thousand men
That, for a fantasy and trick of fame
Go to their graves like beds, fight for a plot
Whereon the numbers cannot try the cause,
Which is not tomb enough and continent
To hide the slain? O, from this time forth
My thoughts be bloody, or be nothing worth!
(4.4.46-69)
This is a major turning point for Hamlet. As he watches Fortinbras' army march across Denmark, he contemplates the fact that so many men will lose their lives fighting for an insignificant and tiny piece of territory, which is nothing more than an "eggshell." At the same time, Hamlet feels a sense of shame that he (a man who has a very good reason to fight), does nothing about the fact that his father has been "kill'd" and his mother has been "stain'd." It is in this very moment that Hamlet's thoughts turn bloody as he sets a direct course for revenge.