I'm not using a rigorous definition, but essentially, consider two outcomes, each affecting 100 people:

  1. Every person accrues $10
  2. One person, "Bob", accrues $100, everyone else accrues $1

Generally speaking, outcome 1 has higher overall benefits, but outcome 2 is better for Bob. If Bob is the decision-maker, it's in Bob's interest to pick outcome 2, even if it's globally worse.

This is what I mean by local vs global interest - roughly, "in the interest of a given individual" vs "the best outcome across all individuals."