Crab mentality

Crab mentality, also known as crab theory, crabs in a bucket (also barrel, basket, or pot) mentality, or the crab-bucket effect, is a way of thinking best described by the phrase "if I can't have it, neither can you". The metaphor is derived from a pattern of behavior noted in crabs when they are trapped in a bucket. While any one crab could easily escape, its efforts will be undermined by others, ensuring the group's collective demise.
The analogy in human behavior is claimed to be that members of a group will attempt to reduce the self-confidence of any member who achieves success beyond the others, out of envy, resentment, spite, conspiracy, or competitive feelings, to halt their progress.
Effect on performance.
Crab mentality affects performance in an organization as humans behave in similar manner as the crabs particularly within social teams. The impact of crab mentality on performance was quantified by a New Zealand study in 2015 which demonstrated up to an 18% average exam result improvement for students when their grades were reported in a way that prevented others from knowing their position in published rankings.