Crab mentality
Crab mentality, also known as crab theory, crabs in a bucket mentality, or the crab-bucket effect, describes the mindset of people who try to prevent others from gaining a favorable position, even if attaining such position would not directly impact those trying to stop them. It is usually summarized with the phrase "If I can't have it, neither can you".
The metaphor is derived from anecdotal claims about the behavior of crabs contained in an open bucket: if a crab starts to climb out, it will be pulled back in by the others, ensuring the group's collective demise.
The analogous theory in human behavior is that members of a group will attempt to reduce the self-confidence of any member who achieves success beyond others, out of envy, jealousy, resentment, spite, conspiracy, or competitive feelings, in order to halt their progress.