In Aristotle's Poetics, he argues that the protagonist of a tragedy should be a "man who is not eminently good and just, yet whose misfortune is brought about not by vice or depravity, but by some error or frailty." This means that the hero should not be a perfect person, but should instead have some flaws or weaknesses. These flaws are not necessarily bad in themselves, but they can lead to the hero's downfall if they are not properly managed.
For example, in the tragedy of Oedipus Rex, the protagonist Oedipus is a good and just man. However, he also has a flaw: he is too quick to anger and make rash decisions. This flaw leads him to kill his father and marry his mother, unknowingly committing the crimes of patricide and incest. Oedipus's downfall is not solely the result of his flaws, but it is also the result of the circumstances he finds himself in.
The same is true of other tragic heroes, such as Hamlet, Othello, and Macbeth. Each of these heroes has flaws or weaknesses that contribute to their downfall, but it is also their interactions with the world around them that ultimately seal their fate.
Therefore, the downfall and destruction of a hero in tragedy is not primarily the result of tragic his or her character. Rather, it is the hero's interaction with the world around them, and the choices they make in response to those circumstances, that ultimately lead to their tragic fate.