By contrasting Walrasian tâtonnement (trial and error) with Vilfredo Pareto’s marchandage (bargaining), this contribution examines Pareto’s position on the question of the stability of general equilibrium and suggests an explanation for the abandonment of his intuition by modern theorists. In Pareto’s terms, bargaining is merely a logical first approximation with no connection to the reality of markets in historical times. Asking why Pareto did not consider it useful to develop his idea of marchandage also helps clarify the status of his pure theory. If it had not been neglected by general equilibrium theorists, his refusal to integrate a stability theorem would perhaps have allowed economic theory to save itself more than thirty years of an exhausting labor leading finally to the negative results of Hugo F. Sonnenschein, Ricardo Mantel and Gérard Debreu.