Delving into the $a_4$ coefficient felt like leafing through a familiar playbook, yet the numbers still carried a thrill when the SymPy script returned $1/10$. Computing the Jarlskog invariant reminded me how subtly the CKM matrix encodes CP violation, and the near meeting of gauge couplings at $10^{16}\,\text{GeV}$ keeps the dream of grand unification alive despite the lingering mismatch.