IDIOMS

glass-half-empty

(idiomatic, of a person) pessimistic

Example: 2006, Laura Klepacki, Avon: Building The World's Premier Company For Women
  Susan Kropf, the company's president and chief operating officer, says that while the management team is “by nature optimistic,” there is a “glass half empty kind of mentality.” Says Kropf. “We always think about what more we could have done, or how we could have done it better.”