Experiments conducted over the past several decades have shown that the cellular structure of detonations is responsible for enhancing the detonability of gaseous detonations in the presence of losses, as compared with that predicted by the classical Zel'dovich-Von Neuman-Doring model for detonations, which neglects the time varying cellular structure of the front. Paradoxically, numerical studies conducted over the past decade have revealed that the propagation of inviscid detonations was hampered if the detonation was allowed to have a cellular structure, the effect increasing with the cellular irregularity. This apparent paradox is discussed in relation to the burning mechanism of unstable cellular detonations established experimentally, which shows that diffusive effects control the reaction of approximately half of the gases passing across the detonation front in unstable cellular detonations. Crown Copyright (C) 2018 Published by Elsevier Inc. on behalf of The Combustion Institute. All rights reserved.