A competitor or person expected to lose or fail; someone in a weaker position facing a much stronger opponent.
Originated in 17th-century dogfighting contexts where the 'underdog' was the weaker dog in a fight. By the 1800s it became metaphorical for anyone disadvantaged in a competition.
Stories about underdogs winning (like Rocky or Cinderella) are so popular that psychologists call 'underdog bias' our natural tendency to root for the weaker side—it might be hardwired into how we think about fairness.
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