What characteristic do tragic heroes share? ?
a. they are forced to struggle before ultimately finding happiness
b. they try to change the traditional structures of society
c. their families often suffer because of their mistakes
d. their own actions or decisions cause their downfall

The answer is D. The hero's downfall, therefore, is partially her/his own fault, the result of free choice, not of accident or villainy or some overriding, malignant fate.  In fact, the tragedy is usually triggered by some error of judgment or some character flaw that contributes to the hero's lack of perfection noted above.   This error of judgment or character flaw is known as hamartia and is usually translated as "tragic flaw.