What is unjust enrichment under the law? It's understandable if associated with liability for wrongdoing. Apparently, this is not a necessary condition. How does it operate independently of liability for wrongdoing?
Unjust enrichment is an equitable theory of recovery that provides a fallback, for lack of better words, avenue of recovery for situations where no contract actually exists between two parties, but one party has received a benefit. The classic example is: Jane hires Dan to mow her lawn and tells him where her house is. Dan mistakenly mows Bob's lawn next door. Dan has no contract to mow Bob's lawn, but Bob has been unjustly enriched based on Dan having mowed his lawn. In this case Dan would have an equitable claim of unjust enrichment against Bob for the value of his yard services mistakenly provided Bob.
In sum, any time someone receives the benefit from someone else's efforts, where the one providing the benefit mistakenly provides those services in good-faith, the one receiving the benefit has been unjustly enriched.