Some discussion this morning on the Democrats maneuvering in Congress led to this idea:
The Prisoner's Dilemma is a part of game theory where, per wikipedia: that shows why two completely rational individuals might not cooperate, even if it appears that it is in their best interests to do so. In the game, if both players trust each other they can end up with an outcome which is good for both, but if they only look to their own interests with no consideration of the other player they end up with the worst result.
I see Senators Manchin and Sinema (MS) as one player; the progressives as the other player. MS want the infrastructure bill; the progressives want the Biden "Build Back Better" bill. If the two groups cooperate they can get both; if they don't they may get neither. Partially this boils down to how much trust the two parties have in each other, but mainly it rests on whether there's a compromise on the size and contents and tax provisions of the BBB which both can live with.