Step 1: The question asks for the fatal flaw of the man in Periasamy Thooran's poem, "The Empty Heart."
Step 2: The poem tells the story of a man who received a magical pitcher that provided him with gold but could never be filled.
Step 3: The man's insatiable 'greed'—his endless desire for more and more wealth—drove him to sacrifice everything, including his health, family, and ultimately his life, in a futile attempt to fill the pitcher. His downfall was a direct result of his unchecked greed. The marked answer (C) is incorrect; his greed caused him to give up sleep.