Well-rooted in modern commercial law is the idea that the law and the obligations that it enforces should reflect the empirical reality of the relationship between the contracting parties. The Uniform Commercial Code ("Code") champions this tradition by viewing the performance practices formed among the parties throughout their interaction as a primary source for interpreting and supplementing their explicit contracts. The generous recognition of waiver and modifications, as well as the binding force the Code accords to course of performance, course of dealings, and customary trade usages, effectively permits unwritten commercial practices to vary and to erode explicit contractual provisions.
Ben-Shahar, Omri. "Formalism in Commercial Law: The Tentative Case against Flexibility in Commercial Law." U. Chi. L. Rev. 66, no. 3 (1999): 781-820.