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"Is the glass half empty or half full?", and other similar expressions such as the adjectives glass-half-full or glass-half-empty, are idioms which contrast a pessimistic and optimistic outlook on a specific situation or on the world at large. "Half full" means optimistic and "half empty" means pessimistic. The origins of this idea are unclear, but it dates at least to the early 20th century. Josi... Wikipedia