1) Polonius to his son Laertes who is departing for France (1.3.84):
"This above all: to thine own self be true,
And it must follow, as the night the day,
Thou canst not then be false to any man."

The true nature of Hamlet's madness has been an issue of debate for scholars over the centuries. One theory is that Hamlet's madness was for his own protection. In the time period in which Hamlet would have lived, governments functioned through the usage of intricate spying networks. In Hamlet's Denmark, no one is permitted to go unwatched.

ACT II, SCENE 5, LINES 105-111
"Yea, from the table of my memory
I'll wipe away all trivial, fond records,
All saws of books, all forms, all pressures past,
That youth and observation copied there,
And thy commandment all alone shall live
Within the book and volume of my brain,
Unmixed with baser matter."

Hamlet: Prince of Denmark, son of Queen Gertrude and the late King Hamlet. He is believed to be mad following the death of his father. He is greatly disturbed by the hasty marriage of his mother to his uncle especially since he considers the relationship to be incestuous.