This lecture is the second part of "The Joy of the S-Matrix" series presented by Francesco Riva from the University of Geneva as part of the KITP Program "What is Particle Theory?" (#particles25). Dive into this field-spanning exploration of particle theory that combines formal, computational, and phenomenological approaches to address central questions in particle physics. The program aims to accelerate progress toward long-standing goals while potentially generating entirely new questions through the union of diverse perspectives and methods. Running for 1 hour and 31 minutes, this lecture continues the weekly two-part series that examines theoretical developments in particle physics. Connect with the Kavli Institute for Theoretical Physics through their various social media platforms to learn more about their ongoing research and programs.