What evidence supports the fact that Hamlet actually thinks too much and thus causes the tragic ending of Hamlet?
Hamlet "thinking too much" certainly supports my theory of Hamlet's tragic flaw being inaction! There are many examples of times when Hamlet over-thinks a situation. For instance, early on in the play, Hamlet is brooding over his mother's new marriage to his uncle (claiming it incestuous) often right in front of their faces:
A little more than kin, and less than kind! . . . O God, a beast that wants discourse of reason / Would have mourned longer--married with my uncle, / My father's brother, but no more like my father / Than I to Hercules. Within a month, / Ere yet the salt of most unrighteous tears / Had left the flushing in her galled eyes, / She married. (1.2.65,150-156)
Also early on in the play, Hamlet, realizing that Claudius is trying to find out why Hamlet is acting strange, decides to "put an antic disposition on" to confuse his uncle (1.5.172). This certainly exacerbates the situation and, some say, leads to Hamlet's true insanity.
Next, there is the famous scene in the church where Claudius is praying and Hamlet over-thinks his revenge so much that he doesn't go through with it:
Now might I do it pat, now 'a is a-praying, / And now I'll do't. And so 'a 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 to heaven. . . . No. (3.3.73-78,87)
Finally, Hamlet's famous monologue (where he basically contemplates suicide and rationalizes why he is unable to avenge his father's death) is probably the most famous instance of over-thinking this world has ever known:
To be, or not to be: that is the question: / Whether 'tis nobler in the mind to suffer / The slings and arrows of outrageous fortune, / Or to take arms against a sea of troubles, / And by opposing end them. To die, to sleep--/ No more-- . . . Thus conscience does make cowards of us all. (3.1.56-61,83)
Of course, all of these things indirectly cause the tragic ending of Hamlet. If Hamlet hadn't obsessed over his mother's new marriage, the play would have ended before it began. If Hamlet hadn't pretended to act crazy, he wouldn't have become crazy in reality. If Hamlet had killed Claudius in church, the finale would have been in Act 3. If Hamlet had killed himself when he was contemplating suicide, there would have been no Hamlet to participate in the rest of the play. Each instance has the same result: no final fencing match, . . . and no bloodbath. But then again, what fun would that be?!?
When Hamlet hears the traveling actor's monologue regarding Achilles's son, Pyrrhus, and how he came to Troy near the end of the Trojan War to exact revenge on Priam, the king of Troy, for his father's death, it stirs Hamlet's doubts about his own behavior. A good amount of time has passed since his father charged Hamlet with avenging his murder. Still, Hamlet has made no real progress in this endeavor. Hamlet wonders that this speech could make the actor cry, and he asks himself, "What would he do / Had he the motive and the cue for passion / That I have?" (2.2.536-538). In other words, Hamlet has so much more reason to feel and act passionately than this player does, yet the player seems to show more than he. All Hamlet does is think and think, with no real action.
Hamlet concludes that he must be "pigeon-livered and lack gall. . . / or ere this / I should have fatted all the region kites / With this slave's offal" (2.2.554-557). He wonders if it is cowardice that has made him hesitate to punish Claudius; if not, he figures, he would have already fed his guts to the birds. Moreover, he says,
Why, what an ass am I! This is most brave,
That I, the son of a dear father murdered,
Prompted to my revenge by heaven and hell,
Must, like a whore, unpack my heart with words
And fall a-cursing like a very drab,
A scullion! (2.2.560-565)
Therefore, although he has every reason to act decisively, he continues to stand around, incessantly talking about his feelings and cursing too. This helps show how Hamlet feels he has considered too deeply, and this has put the wheels in motion for tragedies to occur.