Globular clusters are not the simple stellar populations we used to think they were. The vast majority of them consists of two main populations, dubbed the 1P (pristine) and 2P (polluted) populations, with distinct light-element chemical abundances. How multiple stellar populations unfold remains a riddle. A decade of observations has shown unambiguously that the fraction of 1P stars in clusters, F_1P, is a decreasing function of their present-day mass. That is, the multiple-stellar-population phenomenon is exacerbated in massive clusters. The present-day distribution of Galactic globular clusters in the (mass, F_1P) space must therefore hold clues regarding the formation of their multiple stellar populations. In this talk, I will decipher this distribution, detailing the processes and parameters shaping it.