Human individuals differ from one another in almost all of their genes due to single nucleotide polymorphisms (SNPs). When the maternal and the paternal genomes become combined in a F1 individual, the two alleles of each gene represent arbitrary combinations. In consequence, individuals show high variability in protein expression. Furthermore, within a proteome, the proteins form networks of protein-protein interactions. These networks differ between individuals in robustness against genetic or/and environmental perturbation due to polymorphisms, which differ in type and composition between individuals, and modify the arrangement of proteins in the proteomic network. As a general conclusion, the robustness of a human individual against diseases may depend on the structure and expression of the protein-protein interaction network that varies in its functional efficiency between individuals due to "network-polymorphisms". This article is part of a Special Issue entitled: 20years of Proteomics in memory of Viatliano Pallini. Guest Editors: Luca Bini, Juan J. Calvete, Natacha Turck, Denis Hochstrasser and Jean-Charles Sanchez.