Most research on ad-hoc wireless networks makes simplifying assumptions about radio propagation. The “Flat Earth” model of the world is surprisingly popular: all radios have circular range, have perfect coverage in that range, and travel on a two-dimensional plane. CMU’s ns-2 radio models are better but still fail to represent many aspects of realistic radio networks, including hills, obstacles, link asymmetries, and unpredictable fading. We briefly argue that key “axioms” of these types of propagation models lead to simulation results that do not adequately reflect real behavior of ad-hoc networks, and hence to network protocols that may not work well (or at all) in reality. We then present a set of 802.11 measurements that clearly demonstrate that these “axioms” are contrary to fact. The broad chasm between simulation and reality calls into question many of results from prior papers, and we summarize with a series of recommendations for researchers considering analytic or simulation models of wireless networks.