When studying basic Microeconomics, I saw a sentence:
it is not possible to make someone better off without making someone else worse off.
Does it mean that it is no way to make you feel happy if not making others feel sad?
It refers to what is known as Pareto efficiency or Pareto optimality, that is:
a state of allocation of resources in which it is impossible to make any one individual better off without making at least one individual worse off.
Pareto efficiency is a minimal notion of efficiency and does not necessarily result in a socially desirable distribution of resources: it makes no statement about equality, or the overall well-being of a society
In game theory terms, we can call it a win-lose situation
Win-lose situations result when only one side perceives the outcome as positive.
I am sure your microeconomics resource would have actually elaborated on it; however, there is a fairly common idiom encapsulating this idea.
One man's loss is another man's gain.
Prov. When one person loses something, another person gets it.
(You can substitute appropriate names or pronouns for the phrases one man's and another man's, as in the second example.)
Mike found a five-dollar bill on the sidewalk. "One man's loss is another man's gain," he thought to himself, as he took the money.
Jane: Andy just got fired. Jill: I know. And Andy's loss is my gain; I'm getting promoted to his job!
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.