The law of the jungle
Definition 1 of 2
Pro Tip 1/3Competition Context
Understand this phrase often relates to ruthless competition where only the strongest prevail. 
He was fired in the first round of layoffs - the law of the jungle is brutal.
Pro Tip 2/3Negative Connotation
This phrase can imply unfair or harsh conditions, suggesting an uncivilized approach to survival or success. 
In the slums, it's the law of the jungle; every day is about survival.
Pro Tip 3/3Not Literal
The phrase is used figuratively to describe situations, not actual jungles or animals. 
Network television is tough - it's the law of the jungle for ratings.