Macbeth, the protagonist in William Shakespeare's play Macbeth, does have a tragic flaw. Essentially, even if one cannot recognize Macbeth's flaw, one must exist based upon the characteristics of the tragic play.
Given that Macbeth has been historically identified as a tragic play, one characteristic of the tragic play is that the "protagonist must be an admirable but flawed character." This tragic flaw is called hamartia.
Even with that being said, one can identify Macbeth's tragic flaw through examining what caused his downfall. Macbeth dies at the end. Prior to his death, Macbeth kills many people. One of the people who Macbeth kills is Duncan. Duncan is the current king. Prior to killing Duncan, Macbeth is ridiculed by his wife based upon the prophecies he heard from the witches (that he will be king). When one backtracks through the play, they are led to this thought/question: why did Macbeth kill the king (which led to,in the end, the death of Macbeth)?
Essentially, Macbeth killed the king because he wanted the throne. He did not stick by his initial thoughts about the throne (seen in I,iii):
If chance will have me king, why, chance may crown me. Without my stir.
Therefore, it was his tragic flaw, his growing ambition, which led to his downfall.