The question of whether COVID protease (SARS-CoV-2 M(pro)) can be blocked by inhibitors has been examined, with a particularly successful performance exhibited by alpha-ketoamide derivative substrates like 13b of Hilgenfeld and co-workers (Zhang, L., et al. Science 2020, 368, 409-412). After the biological characterization, here density functional theory calculations explain not only how inhibitor 13b produces a thermodynamically favorable interaction but also how to reach it kinetically. The controversial and unprovable concept of aromaticity here enjoys being the agent that rationalizes the seemingly innocent role of histidine (His41 of M(pro)). It has a hydrogen bond with the hydroxyl group and is the proton carrier of the thiol of Cys145 at almost zero energy cost that favors the interaction with the inhibitor that acts as a Michael acceptor.