Final answer:
The trait of tragedy where a character with power loses this power or position is called peripeteia, which represents the sudden reversal of fortune experienced by a tragic hero.
Step-by-step explanation:
A trait of tragedy that illustrates a character with power or position who must lose this power or position is known as peripeteia. Peripeteia is the reversal of fortune which occurs to a tragic hero, as Aristotle describes in his poetics. For instance, a classic example of this is when in Antigone, the character Creon, who starts off in a position of great power, faces a downfall as he discovers the tragic death of his son and wife, causing his circumstances to turn upside down abruptly.
While other options like hubris, catharsis, and anagnorisis are relevant to the structure of a tragedy, they do not directly answer the question posed. Hubris is the term that denotes excessive pride and is often the character's fatal flaw leading to their downfall, whereas anagnorisis refers to the recognition or realization moment within the plot. Catharsis, on the other hand, is the emotional release experienced by the audience as a result of the unfolding drama.