Hamlet's lack of self-confidence is a topic scholars have long debated. Hamlet is a different man that his father, an intellectual rather than a warrior. He struggles with coming to terms with the bloody revenge his father demands. Says critic Harold Bloom in Shakespeare: The Invention of the Human:
Hamlet...cannot strike us as a likely avenger, because his intellectual freedom, his capaciousness of spirit, seems so at odds with his Ghost-imposed Mission (392).
We see Hamlet struggle with his sense of self and the imposed self throughout the play. Hamlet wants verification that his mission is legitimate before he will act. He tells Horatio,
If it (the ghost) assume my noble father's person, / I'll speak to it, though hell itself should gape / And bid me hold my peace" (1.2.265-67).
Hamlet continually struggles with his moral compass and cannot bring himself to kill Claudius when he has a clear opportunity:
I do 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" (4.4.46-49).
Yet for all his vacillating, Hamlet is a paradox. When he accidentally kills Polonious, he shows no remorse. He is cruel to the woman he claims to love. Such acts do not mesh with reason.
You might be interested in the free lessons and discussion questions available at eNotes on Hamlet. Just click the first link below.