At-will employment means a firing needs no good reason, which is not the same as no reason being off limits. This article explains the narrow but real set of grounds that make a termination unlawful, why the reason an employer gives matters more than the reason it had, and how a case is actually proved when nobody says the quiet part out loud. It covers severance agreements and the two federal rules that govern what a release can validly waive, the WARN Act, final pay, and continuation coverage. It follows two fictional employees fired the same week with very different outcomes. The practical thesis is that the first seventy-two hours after a termination determine most of what is available afterward.