Carrol
^^^^^ CB: Revolutionaries have _slogans_ or rallying cries of progress, because without enthusiasm , elan, the inspiration to struggle is insufficient to win, inadequate to wage it vigorously.
Thus, the African National Congress has the slogan "The struggle continues; victory is certain !" . That's not a theory, it is a peptalk to action, practice struggle.
The Manifesto declared: "What the bourgeoisie therefore produces, above all, are its own grave-diggers. Its fall and the victory of the proletariat are equally inevitable."
Emphasizing the uncertainty or contingency of progress or revolution , true though it may be, doesn't do much to inspire the practice and struggle that is necessary to achieve progress or revolutionary change.
Revolutionaries have revolutionary theories (not suprisingly, smile), without which there can be no revolutionary movement either.