Hamlet, by William Shakespeare if full of situation that revolve around "trust:" the presence of it, or more often, its absence.
When the ghost appears to Hamlet, trust is an enormous concern. Is the ghost an "honest" one? If he thinks that the ghost is truthful and kills Claudius when he is actually innocent, Hamlet's soul could be lost to eternal damnation. (Elizabethans believed it an immortal sin to kill a king.) However, at the beginning, Hamlet tells Horatio that the spirit is "honest:"
Touching this vision here,
It is an honest ghost... (I.v.151-152)
Trust is an issue for Hamlet with Ophelia. Realistically, she must comply when her father and the King tell her to spy on Hamlet. Hamlet feels betrayed, while she agonizes over his seeming madness. Because he does not trust her, he is cruel; he tells her to enter the convent.
I did love you once.
Indeed, my lord, you made me believe so.
You should not have believ'd me, for virtue cannot so
inoculate our old stock but we shall relish of it. I lov'd you not.
I was the more deceiv'd.
Get thee to a nunn'ry, why woulds't thou be a breeder of sinners? (III.i.114-121)
Hamlet does not trust in his own ability avenge his father's murder. When the players come to the castle, he berates himself—watching them cry on cue with nothing to motivate their tears, he hates that he has reason to be devastated, and yet does nothing. He wonders if he is a coward.
unpregnant of my cause,
And can say nothing! No, not for a king,
Upon whose property and most dear life
A damn'd defeat was made. Am I a coward? (II.ii.560-565)
Early on in the play, after Hamlet has visited with the ghost, Hamlet makes the men on the battlements swear to keep secret the appearance of the ghost or that they know anything of Hamlet or his behavior, for he says he will act insane:
As I perchance hereafter shall think meet
To put an antic disposition on—
That you, at such times seeing me, never shall...
That you know aught of me (I.v.168-180)
So as Polonius approaches Hamlet to see if he can find what is bothering the prince, Hamlet puts on "an antic disposition" because he is sure Polonius spies for Claudius, and even Gertrude (who he may not be able to trust). Though he speaks as if he is mad, there is some truth in his words, as he wishes Polonius were an honest man:
Do you know me, my lord?
Excellent well. You are a fishmonger.
Not I, my lord.
Then I would you were so honest a man.
Honest, my lord?
Ay, sir. To be honest, as this world goes, is to be one
man picked out of ten thousand. (II.ii.185-191)
Lastly is Hamlet's uncertainty as to whether his mother was in league with Claudius and the murder of Old Hamlet. After the "play within the play," Hamlet confronts his mother.
A bloody deed. Almost as bad, good mother,
As kill a king, and marry with his brother.
As kill a king?
Ay, lady, it was my word...
Hamlet then describes the man to which she is married, and Gertrude seems genuinely guilty about remarrying, and amazed at his words of "murder." This and the appearance of the ghost lead Hamlet to believe he can trust Gertrude:HAMLET:
A murderer and a villain! A slave that is not twentieth part the tithe Of your precedent lord; a vice of kings; A cutpurse of the empire and the rule, That from a shelf the precious diadem stole And put it in his pocket! (III.iv.106-111)