" However, you will need to know about flavors and generations because of the strong constraints on the particles’ properties, which give us vital clues and constraints on the physics that lies beyond the Standard Model. Chief among these constraints is that different flavors of quarks and leptons with the same charges rarely, if ever, turn into one another. "

― Lisa Randall , Warped Passages: Unraveling the Mysteries of the Universe's Hidden Dimensions