A tragic flaw, as its name suggests, is a negative character trait that ultimately leads to a character's downfall. Shakespeare implements tragic flaws in many of his tragedies (Macbeth's ambition, Othello's jealousy, Lear's naivety), and Hamlet is no exception.
Famously, Hamlet's tragic flaw is his hesitancy to act. He is full of indecision throughout the play, as is evidenced in the "To be or not to be" speech. Often, Hamlet uses various excuses to hide his hesitancy. Take this moment for example, when Hamlet is given the chance to kill Claudius but eventually decides not to:
Now might I do it pat. Now he is a-praying.
And now I’ll do ’t. And so he goes to heaven.
And so am I revenged.—That would be scanned.
A villain kills my father, and, for that,
I, his sole son, do this same villain send
Oh, this is hire and salary, not revenge.
He took my father grossly, full of bread,
With all his crimes broad blown, as flush as May.
And how his audit stands who knows save heaven? (3.3.74–83)
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