This profound statement, pulled from the Talmud, is certainly applicable to more than one character in Shakespeare's Hamlet. Certainly, poor Ophelia does not find the truth within herself; instead, in her naivete and vulnerability, she is influenced by her politico father and by the defensive and bitter Hamet. As Robert Burns wrote,
Truth is within ourselves, it takes no rise
From outward things, whate'er you may believe...
Ophelia does take her perception of truth from "outward things" and it destroys her.
Hamlet, of course, finds himself engaged in terrible self-conflict between his melancholy and his fortitude. With the element of the supernatural and such a corrupt Danish court surrounding him, Hamlet finds it difficult, indeed, to know what action to take. His perception of his mother is, of course, skewered by his disgust that she has "lusted" so greatly that she marries her husband's brother so soon after the king's untimely death. Then, with the treachery of Polonius and Rosencrantz and Guildenstern, who are former friends, Hamlet finds himself in a maelstrom of emotion and thought. Throughout the play, his perception of the truth is distorted by his thinking too much rather than thinking too well until the final act in which he listens to Fortinbras. It is then that Fortinbras's words touch what Browning calls "the inner center in us all where truth abides," and Hamlet becomes resolved in his action, declaring himself "Prince of Denmark," regally setting about to remove the corrupt court of Denmark and avenge his father's wrongful death.
The renowned critic Harold Bloom writes,
Hamlet's tragedy is at last the tragedy of personality....Hamlet's only persuasive enemy is Hamlet himself.
It is when Hamlet finally "sees things as they are," when he, as Burns writes, allows "the imprisoned splendour of truth to escape" that all becomes, not rotten in Denmark, but better.
This a great question that speaks of our tendency as humans to read into things based on our own situation and perspective. Often, our "view" of a situation is highly conditioned by our life situation. In this play, we can see that this is true. One of the central challenges that Hamlet has to face is whether to believe the ghost or not, and it is absolutely clear that his depression that we see he is suffering with in Act I scene 2 leads him to believe the Ghost and his words about the reality of King Hamlet's death. However, this is a question that haunts him for the rest of the play as he tries to gain proof and then seems to find what he is looking for after the Mousetrap in Act III scene 2, even though Horatio is far from convinced that they have enough proof to argue that Claudius did the deed. This play appears to show again and again the dangers of reading too much into situations based on our own perspective.