if a situation is dog eat dog, people will do anything to be successful, even if what they do harms other people In showbusiness it's dog eat dog - one day you're a star, the next you've been replaced by younger talent.
Ruthless acquisition or competition, as in With shrinking markets, it's dog eat dog for every company in this field. This contradicts a Latin proverb which maintains that dog does not eat dog, first recorded in English in 1543. Nevertheless, by 1732 it was put as "Dogs are hard drove when they eat dogs" (Thomas Fuller, Gnomologia).