Should you ever have to compensate another person for their having accidently conferred some benefit on you through no instigation of your own?
Imagine that your neighbor contracts with a local house painter to have his house painted on Saturday. The contract calls for the painter to begin painting the home on Saturday at 8:00 a.m. and complete the home painting with his crew by 6:00 p.m. Sunday evening. Imagine further that your home and your neighbor’s home are virtually identical and are the same color. Both you and your neighbor are away for the entire weekend that the painting is to occur. Imagine your neighbor’s surprise to return home and discover that the painter painted your house instead of his. Imagine your own surprise to learn that you may have to pay for the painting despite the fact that you had not previously contracted with the painting contractor under the legal theory of Prevention of Unjust Enrichment, also known as quasi contract.
The theory of unjust enrichment assumes that there is some "enrichment" by virtue of someone's mistake or some other unexpected eventuality. If you are sued on this theory, your best argument is that you have not been unjustly enriched at all, because the color was not one of your choosing, and you could also countersue the contractor for trespass and the damages that you have sustained by virtue of his having painted your house a color not of your choosing. Whether or not your defense would be credible is, of course, up to the finder of fact, whether that be judge or jury.