Aristotle's concept of hubris refers to excessive pride or arrogance, particularly when a character defies the gods or natural order, leading to their downfall. This is commonly seen as a key element in Greek tragedies.
Thus, option (B) is the correct answer as it aligns with Aristotle's definition of hubris, where pride eventually causes a character's ruin.
Option (A), tragic flaw, is too broad and not specific to hubris. While hubris can be a tragic flaw, Aristotle's definition emphasizes pride.
Option (C), ability to imagine the future, and option (D), humble ascetic quality, are unrelated to Aristotle's concept of hubris.
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\boxed{\text{Correct answer: (B)}}
\]