Temperature at any given location evolves with the horizontal transport of warmer or cooler air, the vertical transport of warmer or cooler air, adiabatic compression or expansion, radiation, and effects related to moisture. In the first part of this talk, I will describe a framework that enables an examination of how these contribute to temperatures at different percentiles. We use ERA-5 data to average the different processes conditioned on each temperature percentile and evaluate their relative contributions to making temperatures more or less extreme. Over much of the midlatitude land, horizontal transport of temperature is critical in driving temperatures towards extreme values. Other regions have other dependencies. Because of the dependence of midlatitude temperature extremes on horizontal transport, the idea that quasi-resonant amplification (QRA) of Rossby waves is important for temperature extremes appears plausible. In the second part of the talk, I will describe the proposed QRA mechanism and how it has been applied in the literature thus far. I will then show how we have explored this mechanism in an idealized climate model and found the theory to not actually hold even in this simple case. I will conclude with some thoughts about process-based understanding of extreme events.