If a change from X to Y results in at least one agent better off without making
any agents worse off, we call Y a
relative to X. If no more Pareto improvements are possible, the situation is
said to be Pareto efficient or Pareto optimal.
When thinking about a proposed Pareto improvement, consider the resistance to
change on the part of the people who will implement your proposal. You may
realize that your proposal is no longer a Pareto improvement because of the
non-monetary costs involved.