Shifting the Burden
Burden shifting is a defined mechanism rather than a description of momentum. Establishing a prima facie position may require an opponent to respond, and raising an affirmative defense places its elements on the party asserting it. In most frameworks the burden of persuasion never moves at all, which means a party who treats a successful prima facie showing as a transfer of the ultimate obligation has misread what happened and will under-prepare everything that follows it.
