sides of my intent, but only / Vaulting ambition, which o'erleaps itself / And fall on th' other--" (1.7.25-28). So, while he has a great many reasons to justify not committing the murder, he has only one reason to go through with it: ambition. However, when LadyMacbeth enters the room, just at this moment, he immediately says to her, "We will proceed no further in this business" (1.7.34). Thus, it seems to me that ambition alone is not enough of a catalyst to prompt him to take action because almost as soon as he identifies it, he tries to cancel their plans.

It is only when Lady Macbeth wounds his pride, mocking his bravery and manhood, that he relents. She insists that, if he will not murder Duncan to take the throne, he will have to "live a coward in [his] own esteem," and that when he made the promise to her that they would proceed with their plan, "then [he was] a man" (1.7.47, 56). She implies that he is not a man if he breaks this promise and swears that she would be willing to kill her own child if she had promised him to do so. Thus, it is only when his pride is wounded that Macbeth finally commits fully to the plan to murder Duncan, and so I argue that pride is his true tragic flaw, not ambition.

In addition to retaining the ambition Macbeth described earlier in the play, the very first scene of Act Four seems to show that he is also somewhat credulous, even gullible. This is a trait that we've seen before, however. In Act One, for example, as soon as Macbeth found out that he'd been named Thane of Cawdor, as the Weird Sisters promised, he believed in their prophecies whole-heartedly and never seemed to doubt their motives. Despite their obvious otherworldliness, Macbeth believes them without reservation, unlike his friend (and foil), Banquo, who says,

[...] oftentimes, to win us to our harm,
The instruments of darkness tell us truths,
Win us with honest trifles, to betray 's
In deepest consequence. (1.3.135-138)

Banquo's cautiousness and cynicism regarding the witches' intentions highlights Macbeth's own credulous readiness to believe. He is likewise trusting, to a fault, of the sisters in Act Four. They tell him,

Macbeth shall never vanquished be until
Great Birnam Wood to high Dunsinane Hill
Shall come against him. (4.1.105-107)

Macbeth hears this and believes it to be an assurance of his safety rather than questioning it as an enigmatically-worded statement of destiny. He seems to trust that the sisters are not attempting to manipulate him, though he has little reason to do so.

Act IV of Macbeth opens with the witches conjuring both a literal and a figurative "hell-broth broil."  (1) No longer capable of rational judgments or being able to discriminate good from evil in his paranoia and (2) "vaulting ambition," Macbeth believes what the witches tell him if it serves his purposes, since for Macbeth, now "fair is foul and foul is fair."  So, he takes the advice of the second witch who tells him to be "bloody, bold, and resolute!" by sending his murderers to kill Macduff's family and him in order to ensure that the bloodline of Duncan be arrested. Furthering his paranoia, the show of eight kings and Banquo with a glass in his hand cause Macbeth's blurring of the lines between reality and sinister forces. He believes that he must eradicate the entire family of Macduff. At this point, the paranoic Macbeth begins to lose control as the pointless death of Lady Macduff and her son underscore his loss of any control as well as his descent into evil.

In Act 5 of Macbeth, Macbeth's remaining time as king has grown short, and he realizes that both his time as king and his life are coming to an end.  However, even though Macbeth has this realization, he fails to make amends for his villainy and instead chooses to fight until the last moment.

First, Lady Macbeth has confessed her role in the murders, and she commits suicide because she feels guilty.  But Macbeth says that there is no time to grieve over her death and feels that the approaching English army is more important than the death of his own wife.

Next, most of the Thanes who have been in Macbeth's charge have fled to join Malcolm and the English army.  Macbeth knows that good kings have friends and loyal servants in their old age, but he realizes that now he is all alone.  Again, Macbeth resolves to fight alone rather than make amends.

When Macbeth sees that Birnam wood is indeed "moving" toward Dunsinane, he does not respect the witches' warning and instead focuses on his own blinded interpretation of the third apparition which told him to fear one who is not of woman born.  Macbeth's misinterpretation causes him to be arrogant when deciding to continue in this fight. 

Finally, even after Macduff reveals that he was ripped from his mother's womb, Macbeth says that he will not fall on Malcolm's feet and he resolves to fight until the bitter end.  This combination of ambition, greed, arrogance, and foolhardy willpower is the tragic flaw that leads Macbeth to his end.

In general, in Shakespeare's Macbeth, Macbeth's tragic flaw is his vaulting (or overpowering) ambition for power.

Aristotle defined a tragic hero as a great (accomplished) man, who has to die, and dies because of his own fault—because of a tragic flaw. A "tragic flaw" is defined as:

...the character defect that causes the downfall of the protagonist of a tragedy

It is also known as "hamartia," which is defined as:

...missing the mark, failure, fault, or error

When he plans to kill Duncan, his King, friend, relative and houseguest, Macbeth admits to the one thing that drives him forward:

I have no spur

To prick the sides of my intent, but only

Vaulting ambition... (I.vii.25-27)

Macbeth's desire for power is the only reason he kills Duncan; it is this flaw that causes him to turn his back on the decent man he is at the beginning of the plan (a valiant warrior, loyal subject and friend) to a murderous tyrant who kills not only Duncan, but his best friend and his enemy's wife and children, among others.

Hecate, the queen of the witches, also notes another problem that haunts Macbeth: he believes he cannot be defeated because of the witches' first set of predictions seemingly came true, proving (in his mind) their credibility. Because he feels so safe, Hecate knows that Macbeth will behave foolishly, much to her delight:

He shall spurn fate, scorn death, and bear

His hopes ’bove wisdom, grace, and fear.

And you all know security

Is mortals’ chiefest enemy. (III.v.30-34)

The other flaw in Macbeth's character, found in Act Five, scene four, is based on these two elements. Macbeth is certain that he is protected because he believes he can only be defeated under impossible circumstances. He is so ambitious, that he will not heed news from his lookouts that the woods are moving.

Duncan's son, Malcolm, has given his men orders to camouflage themselves with branches to cover their numbers so Macbeth does not know how many men are in Malcolm's army.

Let every soldier hew him down a bough,

And bear't before him: thereby shall we shadow

The numbers of our host, and make discovery

Err in report of us. (V.iv.6-9)

Because Macbeth is so certain that he is safe, he doesn't consider that if one of the witches' predictions was based on a half-truth, all of their predictions were suspect. And so, he goes into battle, still believing that Macduff cannot hurt him. Macbeth fails to consider that the witches, inherently evil, might actually be working toward his destruction. It is this "false sense of security," and his vaulting ambition that bring about his demise.

Macbeth's most obvious character flaw is his ambition. This drives him to commit the murder in the first place. He admits as much in his soliloquy at the end in Act I, Scene 7:

I have no spur
To prick the sides of my intent, but only
Vaulting ambition, which o'erleaps itself
And falls on the other—

Macbeth's ambition is largely responsible for his destruction, as well as the demise of most of the people around him. Another character flaw of Macbeth's is his willingness to be swayed by his wife and the witches. In the soliloquy quoted above, Macbeth has essentially decided not to go through with the murder of Duncan, but his wife's goading spurs him toward the task. By the end of the play, he has placed so much stock in the witches' prophecies that he genuinely believes no man "of woman born" can destroy him. He does not pause until the bitter end to consider that the witches are essentially toying with him. 

Over the course of the play, we see Macbeth's unnatural rise to power has corrupted him. He is a bloody tyrant, and has Banquo and Macduff's family murdered to solidify his position as monarch. Macbeth's violence is emphasized early in the play — he "unseam'd" the rebel Macdonwald "from the nave to the chaps" in battle. This act, evidence of his valor and loyalty to Duncan early in the play, grimly foreshadows Macbeth's violence later in the play. 

In summary, three of Macbeth's many character flaws are his ambition, credulity, and capacity for violence.

I.  Viewed as a literary work of its age, Shakespeare's Macbeth is primarily developed as a play in which the relations between natural and supernatural, good and evil, and between masculine and feminine are all interconnected, affecting each other. Moreover, in Macbeth these relations are further complicated by Shakespeare as they become ambiguous for the sake of tragic entanglement. Certainly, "Nothing is what is not" and "Fair is foul and foul is fair" are motifs of this play, and they take on tragic meaning within the framework of the Elizabethan Chain of Being in which each element of the universe has a proper place.

For Macbeth, the lines between the supernatural and the natural become blurred as he feels compelled by his "vaulting ambition" (see his soliloquy in 1.7) to accelerate the predictions of the "weird sisters" by killing King Duncan after Duncan has designated his son Malcolm as the future king. As his partner, Lady Macbeth spurs Macbeth in this act of regicide and, in so doing, blurs the lines between masculine and feminine. After his act of murder, Macbeth is plagued with guilt and shaky, so Lady Macbeth assumes the dominant role:

                          ...Infirm of purpose!
Give me the dagger. The sleeping and the dead
Are but as pictures....

My hands are of your color, but I shame
To wear a heart so white. (2.2.52-65)

These last two lines also exemplify the blurring of good and evil as Lady Macbeth feels shame that Macbeth is seemingly a coward while she is not concerned with his being a murderer. The murderous pair, who become doppelgängers, continue in their path of evil and night seems to dominate day as outside Macbeth's castle in Scene 4 of Act II, Ross tells an old man 

By th' clock ’tis day,

And yet dark night strangles the travelling lamp.

Is ’t night’s predominance or the day’s shame

That darkness does the face of Earth entomb

When living light should kiss it? (2.4.6-10)

That will never be.
Who can impress the forest, bid the tree
Unfix his earth-bound root? Sweet bodements, good! 
Rebellious dead, rise never, till the Wood
Of Birnam rise, and our high-placed Macbeth
Shall live the lease of nature...(4.1.98-103)

Macbeth has many character flaws, but the one that is his downfall is his moral decline. As they say, power begets power, and Macbeth is an example of this. He convinces himself that he is the rightful heir to the throne, even though he has to kill the King to be so. At the start of the play, Macbeth is a hero, but he is easily swayed, shamed by his wife, he continues his downfall. His morals become less important to him, and power more important. Macbeth becomes evil because once he slips down that slope he slides all the way down and cannot claw his way back up to moral again.

I think you must have been misled by a typographical error in whatever you were reading. The subject must have been "tragic flaw." This refers to an Aristotlean concept that the ideal character in a tragedy is a essentially noble individual who comes to a tragic end because of a single flaw in his character. In Shakespeare's Macbeth the hero's tragic flaw is generally taken to be blind ambition. Shakespeare probably knew a great deal more about writing plays than Aristotle, since he was a playwright, an actor, a director, a producer, and a part-owner of a theater. Shakespeare evidently followed classic rules when it suited him and disregarded them when he pleased, as can be seen in the liberties he took with the traditional "unities" of time, place and action. Macbeth had more than one flaw in his character. He was henpecked, gullible, treacherous, and an incompetent ruler.