The theme of “The Piece of String” is the injustice of humanity. Maupassant frequently wrote stories about selfishness, envy, wickedness, spite, greed and other negative human qualities.
In Maupassant’s world, virtually everyone is perfidious, a liar and a phony. He persuades his reader to accept his contention that cunning, ferocity, greed and coarseness are more common among men that one would like to accept. As a writer, he appears tormented at man’s painful state of spiritual loneliness, of the bar which separates man from his fellow men, and of the fact that one’s loneliness is more painfully experienced the nearer one is to others.
In “The Piece of String,” an entire village makes a humble man’s life miserable by accusing him of theft. He tries relentlessly, but unsuccessfully, to persuade them that he was merely picking up a piece of string. The villagers refuse to believe him not as much because they are convinced of his guilt, but rather because they enjoy venting their spite on this humble, defenseless man.
Maupassant was profoundly influenced by the pessimistic German philosopher, Artur Schopenhauer, who had an even lower opinion of human nature. "The Piece of String" might be compared with Shirley Jackson's story "The Lottery" and with Maupassant's famous story "Boule de Suif," according to eNotes.com.