Zero-sum game [1] is the root term. An example is playing poker or similar (without any outside sponsorship or the like) - no matter how well we all play, there's no way for our combined wealth to be greater (or lower) at the end than it was at the beginning. Zero-sum thinking or mind set or whatever is the assumption that a situation is a zero-sum game, which may or may not be true.

[1] https://en.wikipedia.org/wiki/Zero-sum_game