In Act 4, Scene 4 of Hamlet, Hamlet runs into Fortinbras and his army preparing to fight and take over a seemingly worthless portion of Poland. Hamlet is dumbfounded that "two thousand souls and twenty thousand ducats" seems like too much to pay for this land. However, this realization...
leads Hamlet to think that if these men are willing to fight and die for their country, shouldn't he be willing to do the same?
The soliloquy begins with Hamlet realizing that all the events have led him to believe that he needs to seek his revenge. A man who marks time (one who just performs the duty of life by eating, sleeping, and so on) is no good to anyone. God has created us for a reason, and it is up to each person to fulfill it:
How all occasions do inform against me, And spur my dull revenge! What is a man If his chief good and market of his time Be but to sleep and feed? A beast, no more. Sure, he that made us with such large discourse, Looking before and after, gave us not That capability and godlike reason To fust in us unused.
He continues asking himself what is the benefit of being alive to say he should have done this deed instead of actually doing it. He knows he has the "ambition," power, and ability, so he must do it. He refers back to Fortinbras ("a delicate and tender prince") who is leading the men into battle to fight for something as thin and delicate as an eggshell, but they are doing it because it is what they are supposed to do.
And ever three parts coward—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.
Hamlet reminds the audience that being great doesn't just mean fighting because reason calls for it: it means you fight for honor.
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.
Hamlet knows he has a reason to fight. His father was murdered, his mother's honor stained when she married his brother, and he has watched the enemy march their soldiers to fight (and die) for a piece of land so small it couldn't hold all of their burials:
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?
Hamlet's final thoughts show that he is finally resolved to get his revenge. If his thoughts aren't solely about getting revenge ("bloody"), then they are worthless:
Oh, from this time forth,
My thoughts be bloody, or be nothing worth!