In 2013, the IceCube Neutrino Observatory discovered the first strong evidence for a nearly-isotropic astrophysical neutrino background at energies exceeding 1 PeV, presumably associated with the unknown accelerators of high-energy cosmic rays. Almost 8 years later, the origin of these neutrinos remains a mystery. The background is, within measurement uncertainties, uncorrelated with any of the standard catalog of high-energy sources (our galaxy, blazars, gamma-ray bursts, etc.), challenging explanations involving simple models. The 2017 detection of neutrino emission from the blazar TXS 0506+056 has only deepened the mystery. In this talk, I will discuss the potential of neutrinos to clarify our view of the universe, the current state of our knowledge, and the next steps in our experimental program to discover what these data are telling us about physics and the universe.