What is Hamlet's flaw , which he himself indirectly mentions at the end of this monologue "to be or not to be " ?

Hamlet's "To Be, or Not To Be" soliloquy is interesting for several reasons, among which is its revelation of Hamlet's inner character.  Unlike earlier soliloquies,  this one is more rational, calm, and logical.  He systematically picks apart the debate between killing oneself or enduring the many pains of life.  

Ultimately, Hamlet chooses to live rather than to risk the afterlife, which, no matter what one's faith, is a vast mystery.  Hamlet's sums it up...

Hamlet's "To Be, or Not To Be" soliloquy is interesting for several reasons, among which is its revelation of Hamlet's inner character.  Unlike earlier soliloquies,  this one is more rational, calm, and logical.  He systematically picks apart the debate between killing oneself or enduring the many pains of life.  

Ultimately, Hamlet chooses to live rather than to risk the afterlife, which, no matter what one's faith, is a vast mystery.  Hamlet's sums it up when he says "Thus conscience does make cowards of us all."  The meaning here leads to the revelation of his flaw.  Hamlet is a thinker.  He thinks too much, and in doing so, he talks himself out of any substantial action as expressed in his words, "Thus the native hue of resolution is sicklied over with the pale cast of thought..." (III,i). The fire of swift action, in this case, turns pale with the realization of the outcome.  

Sadly for him, Hamlet is a man of thought, not a man of action.  It is this tendency that renders him incapable of following through with his revenge plan.