In the video, however, the whip — with body language that can best be described as plaintive — is making his case to a recalcitrant Conservative lawmaker.

Their exchange is along these lines:

Whip: “Are you feeling any better about the deal on Tuesday? Have we got your support?”

Lawmaker: “No.”

Whip: “O.K.”

Lawmaker: “In a word.”

So that’s where we are. With four days to go until Parliament votes on the government’s plan to leave the E.U., Prime Minister Theresa May and her increasingly desperate team are scrambling to persuade hard-line Brexiteers that her compromise is the best they’re going to get. This means they must let go of whatever vision they had of an ideal outcome, a process one of her allies has described as “shooting the unicorns.”

This is a familiar challenge in negotiations. Game theorists like to use the example of the conquistador Hernán Cortés, who in 1519 attacked the coast of Mexico with a small force. To ensure that Spanish troops would not retreat in the face of a large Aztec counterattack, Cortés ordered them to burn their ships, leaving them no alternative to victory in battle.

“She should say, ‘Dear Brexiteers, your ships are burning, they are gone,’” Marcus Schreiber, an economist who uses game theory to advise executives on negotiations, said of Mrs. May.