From “The Power of the Actor”, by Ivana Chubbuck: Page 51.
Don’t ever admit defeat. There’s always a possibility that you will be able to overcome an OBSTACLE. Even if the chances are small, know that there’s always hope. The person who gives up too easily is often perceived by the audience as a loser. You always want to act from a winning, anything’s-possible point of view. The scene ends when your fight to overcome OBSTACLES to accomplish your SCENE OBJECTIVE ceases. This means if the scene isn’t over, and your fight to overcome conflict stops, the forward motion is arrested and the audience will cease to care anymore. So always keep in mind that it’s not over ’til it’s over. Continue the struggle to overcome your OBSTACLES even a few beats after you exit, the director says, “Cut” or the curtain comes down.